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![Sagi Grimberg](/assets/img/avatar_default.png)
In order to allow sleeping during mmu notifier calls, we need to avoid invoking them under the page table spinlock. This patch solves the problem by calling invalidate_page notification after releasing the lock (but before freeing the page itself), or by wrapping the page invalidation with calls to invalidate_range_begin and invalidate_range_end. To prevent accidental changes to the invalidate_range_end arguments after the call to invalidate_range_begin, the patch introduces a convention of saving the arguments in consistently named locals: unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ ... mmun_start = ... mmun_end = ... mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); ... mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); The patch changes code to use this convention for all calls to mmu_notifier_invalidate_range_start/end, except those where the calls are close enough so that anyone who glances at the code can see the values aren't changing. This patchset is a preliminary step towards on-demand paging design to be added to the RDMA stack. Why do we want on-demand paging for Infiniband? Applications register memory with an RDMA adapter using system calls, and subsequently post IO operations that refer to the corresponding virtual addresses directly to HW. Until now, this was achieved by pinning the memory during the registration calls. The goal of on demand paging is to avoid pinning the pages of registered memory regions (MRs). This will allow users the same flexibility they get when swapping any other part of their processes address spaces. Instead of requiring the entire MR to fit in physical memory, we can allow the MR to be larger, and only fit the current working set in physical memory. Why should anyone care? What problems are users currently experiencing? This can make programming with RDMA much simpler. Today, developers that are working with more data than their RAM can hold need either to deregister and reregister memory regions throughout their process's life, or keep a single memory region and copy the data to it. On demand paging will allow these developers to register a single MR at the beginning of their process's life, and let the operating system manage which pages needs to be fetched at a given time. In the future, we might be able to provide a single memory access key for each process that would provide the entire process's address as one large memory region, and the developers wouldn't need to register memory regions at all. Is there any prospect that any other subsystems will utilise these infrastructural changes? If so, which and how, etc? As for other subsystems, I understand that XPMEM wanted to sleep in MMU notifiers, as Christoph Lameter wrote at http://lkml.indiana.edu/hypermail/linux/kernel/0802.1/0460.html and perhaps Andrea knows about other use cases. Scheduling in mmu notifications is required since we need to sync the hardware with the secondary page tables change. A TLB flush of an IO device is inherently slower than a CPU TLB flush, so our design works by sending the invalidation request to the device, and waiting for an interrupt before exiting the mmu notifier handler. Avi said: kvm may be a buyer. kvm::mmu_lock, which serializes guest page faults, also protects long operations such as destroying large ranges. It would be good to convert it into a spinlock, but as it is used inside mmu notifiers, this cannot be done. (there are alternatives, such as keeping the spinlock and using a generation counter to do the teardown in O(1), which is what the "may" is doing up there). [akpm@linux-foundation.orgpossible speed tweak in hugetlb_cow(), cleanups] Signed-off-by: Andrea Arcangeli <andrea@qumranet.com> Signed-off-by: Sagi Grimberg <sagig@mellanox.com> Signed-off-by: Haggai Eran <haggaie@mellanox.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> Cc: Or Gerlitz <ogerlitz@mellanox.com> Cc: Haggai Eran <haggaie@mellanox.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Liran Liss <liranl@mellanox.com> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: Avi Kivity <avi@redhat.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
486 lines
11 KiB
C
486 lines
11 KiB
C
/*
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* linux/mm/filemap_xip.c
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*
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* Copyright (C) 2005 IBM Corporation
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* Author: Carsten Otte <cotte@de.ibm.com>
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*
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* derived from linux/mm/filemap.c - Copyright (C) Linus Torvalds
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*
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*/
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#include <linux/fs.h>
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#include <linux/pagemap.h>
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#include <linux/export.h>
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#include <linux/uio.h>
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#include <linux/rmap.h>
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#include <linux/mmu_notifier.h>
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#include <linux/sched.h>
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#include <linux/seqlock.h>
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#include <linux/mutex.h>
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#include <linux/gfp.h>
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#include <asm/tlbflush.h>
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#include <asm/io.h>
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/*
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* We do use our own empty page to avoid interference with other users
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* of ZERO_PAGE(), such as /dev/zero
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*/
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static DEFINE_MUTEX(xip_sparse_mutex);
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static seqcount_t xip_sparse_seq = SEQCNT_ZERO;
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static struct page *__xip_sparse_page;
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/* called under xip_sparse_mutex */
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static struct page *xip_sparse_page(void)
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{
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if (!__xip_sparse_page) {
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struct page *page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
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if (page)
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__xip_sparse_page = page;
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}
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return __xip_sparse_page;
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}
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/*
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* This is a file read routine for execute in place files, and uses
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* the mapping->a_ops->get_xip_mem() function for the actual low-level
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* stuff.
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*
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* Note the struct file* is not used at all. It may be NULL.
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*/
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static ssize_t
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do_xip_mapping_read(struct address_space *mapping,
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struct file_ra_state *_ra,
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struct file *filp,
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char __user *buf,
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size_t len,
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loff_t *ppos)
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{
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struct inode *inode = mapping->host;
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pgoff_t index, end_index;
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unsigned long offset;
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loff_t isize, pos;
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size_t copied = 0, error = 0;
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BUG_ON(!mapping->a_ops->get_xip_mem);
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pos = *ppos;
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index = pos >> PAGE_CACHE_SHIFT;
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offset = pos & ~PAGE_CACHE_MASK;
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isize = i_size_read(inode);
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if (!isize)
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goto out;
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end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
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do {
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unsigned long nr, left;
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void *xip_mem;
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unsigned long xip_pfn;
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int zero = 0;
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/* nr is the maximum number of bytes to copy from this page */
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nr = PAGE_CACHE_SIZE;
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if (index >= end_index) {
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if (index > end_index)
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goto out;
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nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
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if (nr <= offset) {
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goto out;
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}
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}
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nr = nr - offset;
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if (nr > len - copied)
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nr = len - copied;
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error = mapping->a_ops->get_xip_mem(mapping, index, 0,
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&xip_mem, &xip_pfn);
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if (unlikely(error)) {
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if (error == -ENODATA) {
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/* sparse */
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zero = 1;
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} else
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goto out;
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}
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/* If users can be writing to this page using arbitrary
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* virtual addresses, take care about potential aliasing
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* before reading the page on the kernel side.
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*/
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if (mapping_writably_mapped(mapping))
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/* address based flush */ ;
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/*
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* Ok, we have the mem, so now we can copy it to user space...
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*
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* The actor routine returns how many bytes were actually used..
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* NOTE! This may not be the same as how much of a user buffer
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* we filled up (we may be padding etc), so we can only update
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* "pos" here (the actor routine has to update the user buffer
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* pointers and the remaining count).
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*/
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if (!zero)
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left = __copy_to_user(buf+copied, xip_mem+offset, nr);
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else
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left = __clear_user(buf + copied, nr);
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if (left) {
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error = -EFAULT;
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goto out;
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}
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copied += (nr - left);
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offset += (nr - left);
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index += offset >> PAGE_CACHE_SHIFT;
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offset &= ~PAGE_CACHE_MASK;
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} while (copied < len);
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out:
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*ppos = pos + copied;
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if (filp)
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file_accessed(filp);
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return (copied ? copied : error);
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}
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ssize_t
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xip_file_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
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{
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if (!access_ok(VERIFY_WRITE, buf, len))
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return -EFAULT;
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return do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
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buf, len, ppos);
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}
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EXPORT_SYMBOL_GPL(xip_file_read);
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/*
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* __xip_unmap is invoked from xip_unmap and
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* xip_write
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*
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* This function walks all vmas of the address_space and unmaps the
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* __xip_sparse_page when found at pgoff.
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*/
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static void
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__xip_unmap (struct address_space * mapping,
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unsigned long pgoff)
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{
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struct vm_area_struct *vma;
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struct mm_struct *mm;
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unsigned long address;
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pte_t *pte;
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pte_t pteval;
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spinlock_t *ptl;
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struct page *page;
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unsigned count;
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int locked = 0;
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count = read_seqcount_begin(&xip_sparse_seq);
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page = __xip_sparse_page;
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if (!page)
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return;
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retry:
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mutex_lock(&mapping->i_mmap_mutex);
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vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
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mm = vma->vm_mm;
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address = vma->vm_start +
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((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
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BUG_ON(address < vma->vm_start || address >= vma->vm_end);
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pte = page_check_address(page, mm, address, &ptl, 1);
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if (pte) {
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/* Nuke the page table entry. */
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flush_cache_page(vma, address, pte_pfn(*pte));
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pteval = ptep_clear_flush(vma, address, pte);
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page_remove_rmap(page);
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dec_mm_counter(mm, MM_FILEPAGES);
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BUG_ON(pte_dirty(pteval));
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pte_unmap_unlock(pte, ptl);
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/* must invalidate_page _before_ freeing the page */
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mmu_notifier_invalidate_page(mm, address);
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page_cache_release(page);
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}
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}
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mutex_unlock(&mapping->i_mmap_mutex);
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if (locked) {
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mutex_unlock(&xip_sparse_mutex);
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} else if (read_seqcount_retry(&xip_sparse_seq, count)) {
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mutex_lock(&xip_sparse_mutex);
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locked = 1;
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goto retry;
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}
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}
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/*
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* xip_fault() is invoked via the vma operations vector for a
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* mapped memory region to read in file data during a page fault.
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*
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* This function is derived from filemap_fault, but used for execute in place
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*/
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static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
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{
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struct file *file = vma->vm_file;
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struct address_space *mapping = file->f_mapping;
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struct inode *inode = mapping->host;
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pgoff_t size;
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void *xip_mem;
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unsigned long xip_pfn;
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struct page *page;
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int error;
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/* XXX: are VM_FAULT_ codes OK? */
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again:
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size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
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if (vmf->pgoff >= size)
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return VM_FAULT_SIGBUS;
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error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
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&xip_mem, &xip_pfn);
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if (likely(!error))
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goto found;
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if (error != -ENODATA)
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return VM_FAULT_OOM;
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/* sparse block */
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if ((vma->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
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(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) &&
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(!(mapping->host->i_sb->s_flags & MS_RDONLY))) {
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int err;
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/* maybe shared writable, allocate new block */
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mutex_lock(&xip_sparse_mutex);
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error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 1,
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&xip_mem, &xip_pfn);
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mutex_unlock(&xip_sparse_mutex);
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if (error)
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return VM_FAULT_SIGBUS;
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/* unmap sparse mappings at pgoff from all other vmas */
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__xip_unmap(mapping, vmf->pgoff);
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found:
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err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address,
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xip_pfn);
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if (err == -ENOMEM)
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return VM_FAULT_OOM;
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/*
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* err == -EBUSY is fine, we've raced against another thread
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* that faulted-in the same page
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*/
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if (err != -EBUSY)
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BUG_ON(err);
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return VM_FAULT_NOPAGE;
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} else {
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int err, ret = VM_FAULT_OOM;
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mutex_lock(&xip_sparse_mutex);
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write_seqcount_begin(&xip_sparse_seq);
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error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
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&xip_mem, &xip_pfn);
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if (unlikely(!error)) {
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write_seqcount_end(&xip_sparse_seq);
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mutex_unlock(&xip_sparse_mutex);
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goto again;
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}
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if (error != -ENODATA)
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goto out;
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/* not shared and writable, use xip_sparse_page() */
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page = xip_sparse_page();
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if (!page)
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goto out;
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err = vm_insert_page(vma, (unsigned long)vmf->virtual_address,
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page);
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if (err == -ENOMEM)
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goto out;
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ret = VM_FAULT_NOPAGE;
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out:
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write_seqcount_end(&xip_sparse_seq);
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mutex_unlock(&xip_sparse_mutex);
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return ret;
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}
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}
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static const struct vm_operations_struct xip_file_vm_ops = {
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.fault = xip_file_fault,
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.page_mkwrite = filemap_page_mkwrite,
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.remap_pages = generic_file_remap_pages,
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};
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int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
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{
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BUG_ON(!file->f_mapping->a_ops->get_xip_mem);
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file_accessed(file);
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vma->vm_ops = &xip_file_vm_ops;
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vma->vm_flags |= VM_MIXEDMAP;
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return 0;
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}
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EXPORT_SYMBOL_GPL(xip_file_mmap);
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static ssize_t
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__xip_file_write(struct file *filp, const char __user *buf,
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size_t count, loff_t pos, loff_t *ppos)
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{
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struct address_space * mapping = filp->f_mapping;
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const struct address_space_operations *a_ops = mapping->a_ops;
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struct inode *inode = mapping->host;
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long status = 0;
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size_t bytes;
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ssize_t written = 0;
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BUG_ON(!mapping->a_ops->get_xip_mem);
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do {
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unsigned long index;
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unsigned long offset;
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size_t copied;
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void *xip_mem;
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unsigned long xip_pfn;
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offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
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index = pos >> PAGE_CACHE_SHIFT;
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bytes = PAGE_CACHE_SIZE - offset;
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if (bytes > count)
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bytes = count;
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status = a_ops->get_xip_mem(mapping, index, 0,
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&xip_mem, &xip_pfn);
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if (status == -ENODATA) {
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/* we allocate a new page unmap it */
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mutex_lock(&xip_sparse_mutex);
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status = a_ops->get_xip_mem(mapping, index, 1,
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&xip_mem, &xip_pfn);
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mutex_unlock(&xip_sparse_mutex);
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if (!status)
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/* unmap page at pgoff from all other vmas */
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__xip_unmap(mapping, index);
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}
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if (status)
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break;
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copied = bytes -
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__copy_from_user_nocache(xip_mem + offset, buf, bytes);
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if (likely(copied > 0)) {
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status = copied;
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if (status >= 0) {
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written += status;
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count -= status;
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pos += status;
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buf += status;
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}
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}
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if (unlikely(copied != bytes))
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if (status >= 0)
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status = -EFAULT;
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if (status < 0)
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break;
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} while (count);
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*ppos = pos;
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/*
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* No need to use i_size_read() here, the i_size
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* cannot change under us because we hold i_mutex.
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*/
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if (pos > inode->i_size) {
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i_size_write(inode, pos);
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mark_inode_dirty(inode);
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}
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return written ? written : status;
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}
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ssize_t
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xip_file_write(struct file *filp, const char __user *buf, size_t len,
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loff_t *ppos)
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{
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struct address_space *mapping = filp->f_mapping;
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struct inode *inode = mapping->host;
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size_t count;
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loff_t pos;
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ssize_t ret;
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sb_start_write(inode->i_sb);
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mutex_lock(&inode->i_mutex);
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if (!access_ok(VERIFY_READ, buf, len)) {
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ret=-EFAULT;
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goto out_up;
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}
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pos = *ppos;
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count = len;
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/* We can write back this queue in page reclaim */
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current->backing_dev_info = mapping->backing_dev_info;
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ret = generic_write_checks(filp, &pos, &count, S_ISBLK(inode->i_mode));
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if (ret)
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goto out_backing;
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if (count == 0)
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goto out_backing;
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ret = file_remove_suid(filp);
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if (ret)
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goto out_backing;
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ret = file_update_time(filp);
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if (ret)
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goto out_backing;
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ret = __xip_file_write (filp, buf, count, pos, ppos);
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out_backing:
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current->backing_dev_info = NULL;
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out_up:
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mutex_unlock(&inode->i_mutex);
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sb_end_write(inode->i_sb);
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return ret;
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}
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EXPORT_SYMBOL_GPL(xip_file_write);
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/*
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* truncate a page used for execute in place
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* functionality is analog to block_truncate_page but does use get_xip_mem
|
|
* to get the page instead of page cache
|
|
*/
|
|
int
|
|
xip_truncate_page(struct address_space *mapping, loff_t from)
|
|
{
|
|
pgoff_t index = from >> PAGE_CACHE_SHIFT;
|
|
unsigned offset = from & (PAGE_CACHE_SIZE-1);
|
|
unsigned blocksize;
|
|
unsigned length;
|
|
void *xip_mem;
|
|
unsigned long xip_pfn;
|
|
int err;
|
|
|
|
BUG_ON(!mapping->a_ops->get_xip_mem);
|
|
|
|
blocksize = 1 << mapping->host->i_blkbits;
|
|
length = offset & (blocksize - 1);
|
|
|
|
/* Block boundary? Nothing to do */
|
|
if (!length)
|
|
return 0;
|
|
|
|
length = blocksize - length;
|
|
|
|
err = mapping->a_ops->get_xip_mem(mapping, index, 0,
|
|
&xip_mem, &xip_pfn);
|
|
if (unlikely(err)) {
|
|
if (err == -ENODATA)
|
|
/* Hole? No need to truncate */
|
|
return 0;
|
|
else
|
|
return err;
|
|
}
|
|
memset(xip_mem + offset, 0, length);
|
|
return 0;
|
|
}
|
|
EXPORT_SYMBOL_GPL(xip_truncate_page);
|