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![Suren Baghdasaryan](/assets/img/avatar_default.png)
walk_page_range() and friends often operate under write-locked mmap_lock. With introduction of vma locks, the vmas have to be locked as well during such walks to prevent concurrent page faults in these areas. Add an additional member to mm_walk_ops to indicate locking requirements for the walk. The change ensures that page walks which prevent concurrent page faults by write-locking mmap_lock, operate correctly after introduction of per-vma locks. With per-vma locks page faults can be handled under vma lock without taking mmap_lock at all, so write locking mmap_lock would not stop them. The change ensures vmas are properly locked during such walks. A sample issue this solves is do_mbind() performing queue_pages_range() to queue pages for migration. Without this change a concurrent page can be faulted into the area and be left out of migration. Link: https://lkml.kernel.org/r/20230804152724.3090321-2-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org> Suggested-by: Jann Horn <jannh@google.com> Cc: David Hildenbrand <david@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Laurent Dufour <ldufour@linux.ibm.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Michel Lespinasse <michel@lespinasse.org> Cc: Peter Xu <peterx@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
614 lines
17 KiB
C
614 lines
17 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Copyright 2013 Red Hat Inc.
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*
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* Authors: Jérôme Glisse <jglisse@redhat.com>
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*/
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/*
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* Refer to include/linux/hmm.h for information about heterogeneous memory
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* management or HMM for short.
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*/
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#include <linux/pagewalk.h>
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#include <linux/hmm.h>
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#include <linux/init.h>
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#include <linux/rmap.h>
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#include <linux/swap.h>
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#include <linux/slab.h>
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#include <linux/sched.h>
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#include <linux/mmzone.h>
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#include <linux/pagemap.h>
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#include <linux/swapops.h>
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#include <linux/hugetlb.h>
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#include <linux/memremap.h>
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#include <linux/sched/mm.h>
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#include <linux/jump_label.h>
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#include <linux/dma-mapping.h>
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#include <linux/mmu_notifier.h>
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#include <linux/memory_hotplug.h>
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#include "internal.h"
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struct hmm_vma_walk {
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struct hmm_range *range;
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unsigned long last;
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};
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enum {
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HMM_NEED_FAULT = 1 << 0,
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HMM_NEED_WRITE_FAULT = 1 << 1,
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HMM_NEED_ALL_BITS = HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT,
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};
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static int hmm_pfns_fill(unsigned long addr, unsigned long end,
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struct hmm_range *range, unsigned long cpu_flags)
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{
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unsigned long i = (addr - range->start) >> PAGE_SHIFT;
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for (; addr < end; addr += PAGE_SIZE, i++)
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range->hmm_pfns[i] = cpu_flags;
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return 0;
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}
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/*
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* hmm_vma_fault() - fault in a range lacking valid pmd or pte(s)
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* @addr: range virtual start address (inclusive)
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* @end: range virtual end address (exclusive)
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* @required_fault: HMM_NEED_* flags
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* @walk: mm_walk structure
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* Return: -EBUSY after page fault, or page fault error
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*
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* This function will be called whenever pmd_none() or pte_none() returns true,
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* or whenever there is no page directory covering the virtual address range.
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*/
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static int hmm_vma_fault(unsigned long addr, unsigned long end,
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unsigned int required_fault, struct mm_walk *walk)
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{
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struct hmm_vma_walk *hmm_vma_walk = walk->private;
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struct vm_area_struct *vma = walk->vma;
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unsigned int fault_flags = FAULT_FLAG_REMOTE;
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WARN_ON_ONCE(!required_fault);
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hmm_vma_walk->last = addr;
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if (required_fault & HMM_NEED_WRITE_FAULT) {
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if (!(vma->vm_flags & VM_WRITE))
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return -EPERM;
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fault_flags |= FAULT_FLAG_WRITE;
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}
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for (; addr < end; addr += PAGE_SIZE)
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if (handle_mm_fault(vma, addr, fault_flags, NULL) &
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VM_FAULT_ERROR)
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return -EFAULT;
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return -EBUSY;
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}
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static unsigned int hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
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unsigned long pfn_req_flags,
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unsigned long cpu_flags)
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{
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struct hmm_range *range = hmm_vma_walk->range;
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/*
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* So we not only consider the individual per page request we also
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* consider the default flags requested for the range. The API can
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* be used 2 ways. The first one where the HMM user coalesces
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* multiple page faults into one request and sets flags per pfn for
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* those faults. The second one where the HMM user wants to pre-
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* fault a range with specific flags. For the latter one it is a
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* waste to have the user pre-fill the pfn arrays with a default
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* flags value.
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*/
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pfn_req_flags &= range->pfn_flags_mask;
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pfn_req_flags |= range->default_flags;
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/* We aren't ask to do anything ... */
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if (!(pfn_req_flags & HMM_PFN_REQ_FAULT))
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return 0;
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/* Need to write fault ? */
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if ((pfn_req_flags & HMM_PFN_REQ_WRITE) &&
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!(cpu_flags & HMM_PFN_WRITE))
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return HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT;
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/* If CPU page table is not valid then we need to fault */
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if (!(cpu_flags & HMM_PFN_VALID))
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return HMM_NEED_FAULT;
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return 0;
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}
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static unsigned int
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hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
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const unsigned long hmm_pfns[], unsigned long npages,
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unsigned long cpu_flags)
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{
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struct hmm_range *range = hmm_vma_walk->range;
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unsigned int required_fault = 0;
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unsigned long i;
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/*
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* If the default flags do not request to fault pages, and the mask does
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* not allow for individual pages to be faulted, then
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* hmm_pte_need_fault() will always return 0.
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*/
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if (!((range->default_flags | range->pfn_flags_mask) &
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HMM_PFN_REQ_FAULT))
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return 0;
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for (i = 0; i < npages; ++i) {
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required_fault |= hmm_pte_need_fault(hmm_vma_walk, hmm_pfns[i],
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cpu_flags);
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if (required_fault == HMM_NEED_ALL_BITS)
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return required_fault;
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}
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return required_fault;
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}
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static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
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__always_unused int depth, struct mm_walk *walk)
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{
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struct hmm_vma_walk *hmm_vma_walk = walk->private;
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struct hmm_range *range = hmm_vma_walk->range;
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unsigned int required_fault;
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unsigned long i, npages;
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unsigned long *hmm_pfns;
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i = (addr - range->start) >> PAGE_SHIFT;
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npages = (end - addr) >> PAGE_SHIFT;
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hmm_pfns = &range->hmm_pfns[i];
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required_fault =
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hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0);
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if (!walk->vma) {
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if (required_fault)
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return -EFAULT;
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return hmm_pfns_fill(addr, end, range, HMM_PFN_ERROR);
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}
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if (required_fault)
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return hmm_vma_fault(addr, end, required_fault, walk);
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return hmm_pfns_fill(addr, end, range, 0);
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}
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static inline unsigned long hmm_pfn_flags_order(unsigned long order)
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{
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return order << HMM_PFN_ORDER_SHIFT;
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}
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static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
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pmd_t pmd)
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{
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if (pmd_protnone(pmd))
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return 0;
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return (pmd_write(pmd) ? (HMM_PFN_VALID | HMM_PFN_WRITE) :
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HMM_PFN_VALID) |
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hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT);
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}
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
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unsigned long end, unsigned long hmm_pfns[],
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pmd_t pmd)
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{
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struct hmm_vma_walk *hmm_vma_walk = walk->private;
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struct hmm_range *range = hmm_vma_walk->range;
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unsigned long pfn, npages, i;
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unsigned int required_fault;
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unsigned long cpu_flags;
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npages = (end - addr) >> PAGE_SHIFT;
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cpu_flags = pmd_to_hmm_pfn_flags(range, pmd);
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required_fault =
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hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, cpu_flags);
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if (required_fault)
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return hmm_vma_fault(addr, end, required_fault, walk);
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pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
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for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
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hmm_pfns[i] = pfn | cpu_flags;
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return 0;
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}
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#else /* CONFIG_TRANSPARENT_HUGEPAGE */
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/* stub to allow the code below to compile */
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int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
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unsigned long end, unsigned long hmm_pfns[], pmd_t pmd);
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#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
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static inline unsigned long pte_to_hmm_pfn_flags(struct hmm_range *range,
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pte_t pte)
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{
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if (pte_none(pte) || !pte_present(pte) || pte_protnone(pte))
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return 0;
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return pte_write(pte) ? (HMM_PFN_VALID | HMM_PFN_WRITE) : HMM_PFN_VALID;
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}
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static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
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unsigned long end, pmd_t *pmdp, pte_t *ptep,
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unsigned long *hmm_pfn)
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{
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struct hmm_vma_walk *hmm_vma_walk = walk->private;
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struct hmm_range *range = hmm_vma_walk->range;
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unsigned int required_fault;
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unsigned long cpu_flags;
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pte_t pte = ptep_get(ptep);
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uint64_t pfn_req_flags = *hmm_pfn;
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if (pte_none_mostly(pte)) {
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required_fault =
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hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
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if (required_fault)
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goto fault;
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*hmm_pfn = 0;
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return 0;
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}
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if (!pte_present(pte)) {
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swp_entry_t entry = pte_to_swp_entry(pte);
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/*
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* Don't fault in device private pages owned by the caller,
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* just report the PFN.
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*/
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if (is_device_private_entry(entry) &&
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pfn_swap_entry_to_page(entry)->pgmap->owner ==
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range->dev_private_owner) {
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cpu_flags = HMM_PFN_VALID;
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if (is_writable_device_private_entry(entry))
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cpu_flags |= HMM_PFN_WRITE;
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*hmm_pfn = swp_offset_pfn(entry) | cpu_flags;
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return 0;
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}
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required_fault =
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hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
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if (!required_fault) {
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*hmm_pfn = 0;
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return 0;
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}
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if (!non_swap_entry(entry))
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goto fault;
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if (is_device_private_entry(entry))
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goto fault;
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if (is_device_exclusive_entry(entry))
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goto fault;
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if (is_migration_entry(entry)) {
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pte_unmap(ptep);
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hmm_vma_walk->last = addr;
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migration_entry_wait(walk->mm, pmdp, addr);
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return -EBUSY;
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}
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/* Report error for everything else */
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pte_unmap(ptep);
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return -EFAULT;
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}
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cpu_flags = pte_to_hmm_pfn_flags(range, pte);
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required_fault =
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hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
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if (required_fault)
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goto fault;
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/*
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* Bypass devmap pte such as DAX page when all pfn requested
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* flags(pfn_req_flags) are fulfilled.
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* Since each architecture defines a struct page for the zero page, just
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* fall through and treat it like a normal page.
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*/
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if (!vm_normal_page(walk->vma, addr, pte) &&
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!pte_devmap(pte) &&
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!is_zero_pfn(pte_pfn(pte))) {
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if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {
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pte_unmap(ptep);
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return -EFAULT;
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}
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*hmm_pfn = HMM_PFN_ERROR;
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return 0;
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}
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*hmm_pfn = pte_pfn(pte) | cpu_flags;
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return 0;
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fault:
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pte_unmap(ptep);
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/* Fault any virtual address we were asked to fault */
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return hmm_vma_fault(addr, end, required_fault, walk);
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}
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static int hmm_vma_walk_pmd(pmd_t *pmdp,
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unsigned long start,
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unsigned long end,
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struct mm_walk *walk)
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{
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struct hmm_vma_walk *hmm_vma_walk = walk->private;
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struct hmm_range *range = hmm_vma_walk->range;
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unsigned long *hmm_pfns =
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&range->hmm_pfns[(start - range->start) >> PAGE_SHIFT];
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unsigned long npages = (end - start) >> PAGE_SHIFT;
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unsigned long addr = start;
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pte_t *ptep;
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pmd_t pmd;
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again:
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pmd = pmdp_get_lockless(pmdp);
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if (pmd_none(pmd))
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return hmm_vma_walk_hole(start, end, -1, walk);
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if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
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if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) {
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hmm_vma_walk->last = addr;
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pmd_migration_entry_wait(walk->mm, pmdp);
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return -EBUSY;
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}
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return hmm_pfns_fill(start, end, range, 0);
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}
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if (!pmd_present(pmd)) {
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if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
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return -EFAULT;
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return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
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}
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if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {
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/*
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* No need to take pmd_lock here, even if some other thread
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* is splitting the huge pmd we will get that event through
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* mmu_notifier callback.
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*
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* So just read pmd value and check again it's a transparent
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* huge or device mapping one and compute corresponding pfn
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* values.
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*/
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pmd = pmdp_get_lockless(pmdp);
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if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
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goto again;
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return hmm_vma_handle_pmd(walk, addr, end, hmm_pfns, pmd);
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}
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/*
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* We have handled all the valid cases above ie either none, migration,
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* huge or transparent huge. At this point either it is a valid pmd
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* entry pointing to pte directory or it is a bad pmd that will not
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* recover.
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*/
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if (pmd_bad(pmd)) {
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if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
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return -EFAULT;
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return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
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}
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ptep = pte_offset_map(pmdp, addr);
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if (!ptep)
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goto again;
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for (; addr < end; addr += PAGE_SIZE, ptep++, hmm_pfns++) {
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int r;
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r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, hmm_pfns);
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if (r) {
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/* hmm_vma_handle_pte() did pte_unmap() */
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return r;
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}
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}
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pte_unmap(ptep - 1);
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return 0;
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}
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#if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && \
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defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
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static inline unsigned long pud_to_hmm_pfn_flags(struct hmm_range *range,
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pud_t pud)
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{
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if (!pud_present(pud))
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return 0;
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return (pud_write(pud) ? (HMM_PFN_VALID | HMM_PFN_WRITE) :
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HMM_PFN_VALID) |
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hmm_pfn_flags_order(PUD_SHIFT - PAGE_SHIFT);
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}
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static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
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struct mm_walk *walk)
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{
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struct hmm_vma_walk *hmm_vma_walk = walk->private;
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struct hmm_range *range = hmm_vma_walk->range;
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unsigned long addr = start;
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pud_t pud;
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spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma);
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if (!ptl)
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return 0;
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/* Normally we don't want to split the huge page */
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walk->action = ACTION_CONTINUE;
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pud = READ_ONCE(*pudp);
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if (pud_none(pud)) {
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spin_unlock(ptl);
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return hmm_vma_walk_hole(start, end, -1, walk);
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}
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if (pud_huge(pud) && pud_devmap(pud)) {
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unsigned long i, npages, pfn;
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unsigned int required_fault;
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unsigned long *hmm_pfns;
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unsigned long cpu_flags;
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if (!pud_present(pud)) {
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spin_unlock(ptl);
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return hmm_vma_walk_hole(start, end, -1, walk);
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}
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i = (addr - range->start) >> PAGE_SHIFT;
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npages = (end - addr) >> PAGE_SHIFT;
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hmm_pfns = &range->hmm_pfns[i];
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cpu_flags = pud_to_hmm_pfn_flags(range, pud);
|
|
required_fault = hmm_range_need_fault(hmm_vma_walk, hmm_pfns,
|
|
npages, cpu_flags);
|
|
if (required_fault) {
|
|
spin_unlock(ptl);
|
|
return hmm_vma_fault(addr, end, required_fault, walk);
|
|
}
|
|
|
|
pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
|
|
for (i = 0; i < npages; ++i, ++pfn)
|
|
hmm_pfns[i] = pfn | cpu_flags;
|
|
goto out_unlock;
|
|
}
|
|
|
|
/* Ask for the PUD to be split */
|
|
walk->action = ACTION_SUBTREE;
|
|
|
|
out_unlock:
|
|
spin_unlock(ptl);
|
|
return 0;
|
|
}
|
|
#else
|
|
#define hmm_vma_walk_pud NULL
|
|
#endif
|
|
|
|
#ifdef CONFIG_HUGETLB_PAGE
|
|
static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
|
|
unsigned long start, unsigned long end,
|
|
struct mm_walk *walk)
|
|
{
|
|
unsigned long addr = start, i, pfn;
|
|
struct hmm_vma_walk *hmm_vma_walk = walk->private;
|
|
struct hmm_range *range = hmm_vma_walk->range;
|
|
struct vm_area_struct *vma = walk->vma;
|
|
unsigned int required_fault;
|
|
unsigned long pfn_req_flags;
|
|
unsigned long cpu_flags;
|
|
spinlock_t *ptl;
|
|
pte_t entry;
|
|
|
|
ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);
|
|
entry = huge_ptep_get(pte);
|
|
|
|
i = (start - range->start) >> PAGE_SHIFT;
|
|
pfn_req_flags = range->hmm_pfns[i];
|
|
cpu_flags = pte_to_hmm_pfn_flags(range, entry) |
|
|
hmm_pfn_flags_order(huge_page_order(hstate_vma(vma)));
|
|
required_fault =
|
|
hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
|
|
if (required_fault) {
|
|
int ret;
|
|
|
|
spin_unlock(ptl);
|
|
hugetlb_vma_unlock_read(vma);
|
|
/*
|
|
* Avoid deadlock: drop the vma lock before calling
|
|
* hmm_vma_fault(), which will itself potentially take and
|
|
* drop the vma lock. This is also correct from a
|
|
* protection point of view, because there is no further
|
|
* use here of either pte or ptl after dropping the vma
|
|
* lock.
|
|
*/
|
|
ret = hmm_vma_fault(addr, end, required_fault, walk);
|
|
hugetlb_vma_lock_read(vma);
|
|
return ret;
|
|
}
|
|
|
|
pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT);
|
|
for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
|
|
range->hmm_pfns[i] = pfn | cpu_flags;
|
|
|
|
spin_unlock(ptl);
|
|
return 0;
|
|
}
|
|
#else
|
|
#define hmm_vma_walk_hugetlb_entry NULL
|
|
#endif /* CONFIG_HUGETLB_PAGE */
|
|
|
|
static int hmm_vma_walk_test(unsigned long start, unsigned long end,
|
|
struct mm_walk *walk)
|
|
{
|
|
struct hmm_vma_walk *hmm_vma_walk = walk->private;
|
|
struct hmm_range *range = hmm_vma_walk->range;
|
|
struct vm_area_struct *vma = walk->vma;
|
|
|
|
if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)) &&
|
|
vma->vm_flags & VM_READ)
|
|
return 0;
|
|
|
|
/*
|
|
* vma ranges that don't have struct page backing them or map I/O
|
|
* devices directly cannot be handled by hmm_range_fault().
|
|
*
|
|
* If the vma does not allow read access, then assume that it does not
|
|
* allow write access either. HMM does not support architectures that
|
|
* allow write without read.
|
|
*
|
|
* If a fault is requested for an unsupported range then it is a hard
|
|
* failure.
|
|
*/
|
|
if (hmm_range_need_fault(hmm_vma_walk,
|
|
range->hmm_pfns +
|
|
((start - range->start) >> PAGE_SHIFT),
|
|
(end - start) >> PAGE_SHIFT, 0))
|
|
return -EFAULT;
|
|
|
|
hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
|
|
|
|
/* Skip this vma and continue processing the next vma. */
|
|
return 1;
|
|
}
|
|
|
|
static const struct mm_walk_ops hmm_walk_ops = {
|
|
.pud_entry = hmm_vma_walk_pud,
|
|
.pmd_entry = hmm_vma_walk_pmd,
|
|
.pte_hole = hmm_vma_walk_hole,
|
|
.hugetlb_entry = hmm_vma_walk_hugetlb_entry,
|
|
.test_walk = hmm_vma_walk_test,
|
|
.walk_lock = PGWALK_RDLOCK,
|
|
};
|
|
|
|
/**
|
|
* hmm_range_fault - try to fault some address in a virtual address range
|
|
* @range: argument structure
|
|
*
|
|
* Returns 0 on success or one of the following error codes:
|
|
*
|
|
* -EINVAL: Invalid arguments or mm or virtual address is in an invalid vma
|
|
* (e.g., device file vma).
|
|
* -ENOMEM: Out of memory.
|
|
* -EPERM: Invalid permission (e.g., asking for write and range is read
|
|
* only).
|
|
* -EBUSY: The range has been invalidated and the caller needs to wait for
|
|
* the invalidation to finish.
|
|
* -EFAULT: A page was requested to be valid and could not be made valid
|
|
* ie it has no backing VMA or it is illegal to access
|
|
*
|
|
* This is similar to get_user_pages(), except that it can read the page tables
|
|
* without mutating them (ie causing faults).
|
|
*/
|
|
int hmm_range_fault(struct hmm_range *range)
|
|
{
|
|
struct hmm_vma_walk hmm_vma_walk = {
|
|
.range = range,
|
|
.last = range->start,
|
|
};
|
|
struct mm_struct *mm = range->notifier->mm;
|
|
int ret;
|
|
|
|
mmap_assert_locked(mm);
|
|
|
|
do {
|
|
/* If range is no longer valid force retry. */
|
|
if (mmu_interval_check_retry(range->notifier,
|
|
range->notifier_seq))
|
|
return -EBUSY;
|
|
ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
|
|
&hmm_walk_ops, &hmm_vma_walk);
|
|
/*
|
|
* When -EBUSY is returned the loop restarts with
|
|
* hmm_vma_walk.last set to an address that has not been stored
|
|
* in pfns. All entries < last in the pfn array are set to their
|
|
* output, and all >= are still at their input values.
|
|
*/
|
|
} while (ret == -EBUSY);
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL(hmm_range_fault);
|