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679d103319
Patch series "userfaultfd-wp: Support shmem and hugetlbfs", v8.
Overview
========
Userfaultfd-wp anonymous support was merged two years ago. There're quite
a few applications that started to leverage this capability either to take
snapshots for user-app memory, or use it for full user controled swapping.
This series tries to complete the feature for uffd-wp so as to cover all
the RAM-based memory types. So far uffd-wp is the only missing piece of
the rest features (uffd-missing & uffd-minor mode).
One major reason to do so is that anonymous pages are sometimes not
satisfying the need of applications, and there're growing users of either
shmem and hugetlbfs for either sharing purpose (e.g., sharing guest mem
between hypervisor process and device emulation process, shmem local live
migration for upgrades), or for performance on tlb hits.
All these mean that if a uffd-wp app wants to switch to any of the memory
types, it'll stop working. I think it's worthwhile to have the kernel to
cover all these aspects.
This series chose to protect pages in pte level not page level.
One major reason is safety. I have no idea how we could make it safe if
any of the uffd-privileged app can wr-protect a page that any other
application can use. It means this app can block any process potentially
for any time it wants.
The other reason is that it aligns very well with not only the anonymous
uffd-wp solution, but also uffd as a whole. For example, userfaultfd is
implemented fundamentally based on VMAs. We set flags to VMAs showing the
status of uffd tracking. For another per-page based protection solution,
it'll be crossing the fundation line on VMA-based, and it could simply be
too far away already from what's called userfaultfd.
PTE markers
===========
The patchset is based on the idea called PTE markers. It was discussed in
one of the mm alignment sessions, proposed starting from v6, and this is
the 2nd version of it using PTE marker idea.
PTE marker is a new type of swap entry that is ony applicable to file
backed memories like shmem and hugetlbfs. It's used to persist some
pte-level information even if the original present ptes in pgtable are
zapped.
Logically pte markers can store more than uffd-wp information, but so far
only one bit is used for uffd-wp purpose. When the pte marker is
installed with uffd-wp bit set, it means this pte is wr-protected by uffd.
It solves the problem on e.g. file-backed memory mapped ptes got zapped
due to any reason (e.g. thp split, or swapped out), we can still keep the
wr-protect information in the ptes. Then when the page fault triggers
again, we'll know this pte is wr-protected so we can treat the pte the
same as a normal uffd wr-protected pte.
The extra information is encoded into the swap entry, or swp_offset to be
explicit, with the swp_type being PTE_MARKER. So far uffd-wp only uses
one bit out of the swap entry, the rest bits of swp_offset are still
reserved for other purposes.
There're two configs to enable/disable PTE markers:
CONFIG_PTE_MARKER
CONFIG_PTE_MARKER_UFFD_WP
We can set !PTE_MARKER to completely disable all the PTE markers, along
with uffd-wp support. I made two config so we can also enable PTE marker
but disable uffd-wp file-backed for other purposes. At the end of current
series, I'll enable CONFIG_PTE_MARKER by default, but that patch is
standalone and if anyone worries about having it by default, we can also
consider turn it off by dropping that oneliner patch. So far I don't see
a huge risk of doing so, so I kept that patch.
In most cases, PTE markers should be treated as none ptes. It is because
that unlike most of the other swap entry types, there's no PFN or block
offset information encoded into PTE markers but some extra well-defined
bits showing the status of the pte. These bits should only be used as
extra data when servicing an upcoming page fault, and then we behave as if
it's a none pte.
I did spend a lot of time observing all the pte_none() users this time.
It is indeed a challenge because there're a lot, and I hope I didn't miss
a single of them when we should take care of pte markers. Luckily, I
don't think it'll need to be considered in many cases, for example: boot
code, arch code (especially non-x86), kernel-only page handlings (e.g.
CPA), or device driver codes when we're tackling with pure PFN mappings.
I introduced pte_none_mostly() in this series when we need to handle pte
markers the same as none pte, the "mostly" is the other way to write
"either none pte or a pte marker".
I didn't replace pte_none() to cover pte markers for below reasons:
- Very rare case of pte_none() callers will handle pte markers. E.g., all
the kernel pages do not require knowledge of pte markers. So we don't
pollute the major use cases.
- Unconditionally change pte_none() semantics could confuse people, because
pte_none() existed for so long a time.
- Unconditionally change pte_none() semantics could make pte_none() slower
even if in many cases pte markers do not exist.
- There're cases where we'd like to handle pte markers differntly from
pte_none(), so a full replace is also impossible. E.g. khugepaged should
still treat pte markers as normal swap ptes rather than none ptes, because
pte markers will always need a fault-in to merge the marker with a valid
pte. Or the smap code will need to parse PTE markers not none ptes.
Patch Layout
============
Introducing PTE marker and uffd-wp bit in PTE marker:
mm: Introduce PTE_MARKER swap entry
mm: Teach core mm about pte markers
mm: Check against orig_pte for finish_fault()
mm/uffd: PTE_MARKER_UFFD_WP
Adding support for shmem uffd-wp:
mm/shmem: Take care of UFFDIO_COPY_MODE_WP
mm/shmem: Handle uffd-wp special pte in page fault handler
mm/shmem: Persist uffd-wp bit across zapping for file-backed
mm/shmem: Allow uffd wr-protect none pte for file-backed mem
mm/shmem: Allows file-back mem to be uffd wr-protected on thps
mm/shmem: Handle uffd-wp during fork()
Adding support for hugetlbfs uffd-wp:
mm/hugetlb: Introduce huge pte version of uffd-wp helpers
mm/hugetlb: Hook page faults for uffd write protection
mm/hugetlb: Take care of UFFDIO_COPY_MODE_WP
mm/hugetlb: Handle UFFDIO_WRITEPROTECT
mm/hugetlb: Handle pte markers in page faults
mm/hugetlb: Allow uffd wr-protect none ptes
mm/hugetlb: Only drop uffd-wp special pte if required
mm/hugetlb: Handle uffd-wp during fork()
Misc handling on the rest mm for uffd-wp file-backed:
mm/khugepaged: Don't recycle vma pgtable if uffd-wp registered
mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs
Enabling of uffd-wp on file-backed memory:
mm/uffd: Enable write protection for shmem & hugetlbfs
mm: Enable PTE markers by default
selftests/uffd: Enable uffd-wp for shmem/hugetlbfs
Tests
=====
- Compile test on x86_64 and aarch64 on different configs
- Kernel selftests
- uffd-test [0]
- Umapsort [1,2] test for shmem/hugetlb, with swap on/off
[0] https://github.com/xzpeter/clibs/tree/master/uffd-test
[1] https://github.com/xzpeter/umap-apps/tree/peter
[2] https://github.com/xzpeter/umap/tree/peter-shmem-hugetlbfs
This patch (of 23):
Introduces a new swap entry type called PTE_MARKER. It can be installed
for any pte that maps a file-backed memory when the pte is temporarily
zapped, so as to maintain per-pte information.
The information that kept in the pte is called a "marker". Here we define
the marker as "unsigned long" just to match pgoff_t, however it will only
work if it still fits in swp_offset(), which is e.g. currently 58 bits on
x86_64.
A new config CONFIG_PTE_MARKER is introduced too; it's by default off. A
bunch of helpers are defined altogether to service the rest of the pte
marker code.
[peterx@redhat.com: fixup]
Link: https://lkml.kernel.org/r/Yk2rdB7SXZf+2BDF@xz-m1.local
Link: https://lkml.kernel.org/r/20220405014646.13522-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20220405014646.13522-2-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
128 lines
2.9 KiB
C
128 lines
2.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* IBM System z Huge TLB Page Support for Kernel.
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*
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* Copyright IBM Corp. 2008
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* Author(s): Gerald Schaefer <gerald.schaefer@de.ibm.com>
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*/
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#ifndef _ASM_S390_HUGETLB_H
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#define _ASM_S390_HUGETLB_H
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#include <linux/pgtable.h>
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#include <asm/page.h>
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#define hugetlb_free_pgd_range free_pgd_range
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#define hugepages_supported() (MACHINE_HAS_EDAT1)
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void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
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pte_t *ptep, pte_t pte);
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pte_t huge_ptep_get(pte_t *ptep);
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pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
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unsigned long addr, pte_t *ptep);
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/*
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* If the arch doesn't supply something else, assume that hugepage
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* size aligned regions are ok without further preparation.
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*/
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static inline int prepare_hugepage_range(struct file *file,
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unsigned long addr, unsigned long len)
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{
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if (len & ~HPAGE_MASK)
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return -EINVAL;
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if (addr & ~HPAGE_MASK)
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return -EINVAL;
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return 0;
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}
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static inline void arch_clear_hugepage_flags(struct page *page)
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{
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clear_bit(PG_arch_1, &page->flags);
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}
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#define arch_clear_hugepage_flags arch_clear_hugepage_flags
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static inline void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
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pte_t *ptep, unsigned long sz)
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{
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if ((pte_val(*ptep) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
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set_pte(ptep, __pte(_REGION3_ENTRY_EMPTY));
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else
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set_pte(ptep, __pte(_SEGMENT_ENTRY_EMPTY));
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}
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static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
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unsigned long address, pte_t *ptep)
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{
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huge_ptep_get_and_clear(vma->vm_mm, address, ptep);
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}
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static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
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unsigned long addr, pte_t *ptep,
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pte_t pte, int dirty)
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{
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int changed = !pte_same(huge_ptep_get(ptep), pte);
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if (changed) {
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huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
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set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
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}
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return changed;
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}
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static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
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unsigned long addr, pte_t *ptep)
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{
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pte_t pte = huge_ptep_get_and_clear(mm, addr, ptep);
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set_huge_pte_at(mm, addr, ptep, pte_wrprotect(pte));
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}
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static inline pte_t mk_huge_pte(struct page *page, pgprot_t pgprot)
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{
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return mk_pte(page, pgprot);
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}
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static inline int huge_pte_none(pte_t pte)
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{
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return pte_none(pte);
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}
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static inline int huge_pte_none_mostly(pte_t pte)
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{
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return huge_pte_none(pte);
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}
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static inline int huge_pte_write(pte_t pte)
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{
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return pte_write(pte);
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}
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static inline int huge_pte_dirty(pte_t pte)
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{
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return pte_dirty(pte);
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}
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static inline pte_t huge_pte_mkwrite(pte_t pte)
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{
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return pte_mkwrite(pte);
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}
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static inline pte_t huge_pte_mkdirty(pte_t pte)
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{
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return pte_mkdirty(pte);
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}
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static inline pte_t huge_pte_wrprotect(pte_t pte)
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{
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return pte_wrprotect(pte);
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}
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static inline pte_t huge_pte_modify(pte_t pte, pgprot_t newprot)
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{
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return pte_modify(pte, newprot);
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}
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static inline bool gigantic_page_runtime_supported(void)
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{
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return true;
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}
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#endif /* _ASM_S390_HUGETLB_H */
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