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mm/hugetlb: introduce hugetlb_walk()

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huge_pte_offset() is the main walker function for hugetlb pgtables.  The
name is not really representing what it does, though.

Instead of renaming it, introduce a wrapper function called hugetlb_walk()
which will use huge_pte_offset() inside.  Assert on the locks when walking
the pgtable.

Note, the vma lock assertion will be a no-op for private mappings.

Document the last special case in the page_vma_mapped_walk() path where we
don't need any more lock to call hugetlb_walk().

Taking vma lock there is not needed because either: (1) potential callers
of hugetlb pvmw holds i_mmap_rwsem already (from one rmap_walk()), or (2)
the caller will not walk a hugetlb vma at all so the hugetlb code path not
reachable (e.g.  in ksm or uprobe paths).

It's slightly implicit for future page_vma_mapped_walk() callers on that
lock requirement.  But anyway, when one day this rule breaks, one will get
a straightforward warning in hugetlb_walk() with lockdep, then there'll be
a way out.

[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/20221216155229.2043750-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Peter Xu 2022-12-16 10:52:29 -05:00 committed by Andrew Morton
parent dd361e5033
commit 9c67a20704
6 changed files with 60 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
fs/hugetlbfs/inode.c
View File

@ -388,9 +388,7 @@ static bool hugetlb_vma_maps_page(struct vm_area_struct *vma,
{
pte_t *ptep, pte;
ptep = huge_pte_offset(vma->vm_mm, addr,
huge_page_size(hstate_vma(vma)));
ptep = hugetlb_walk(vma, addr, huge_page_size(hstate_vma(vma)));
if (!ptep)
return false;

6
fs/userfaultfd.c
View File

@ -252,14 +252,12 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
unsigned long flags,
unsigned long reason)
{
struct mm_struct *mm = ctx->mm;
pte_t *ptep, pte;
bool ret = true;
mmap_assert_locked(mm);
ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
mmap_assert_locked(ctx->mm);
ptep = hugetlb_walk(vma, address, vma_mmu_pagesize(vma));
if (!ptep)
goto out;

37
include/linux/hugetlb.h
View File

@ -2,6 +2,7 @@
#ifndef _LINUX_HUGETLB_H
#define _LINUX_HUGETLB_H
#include <linux/mm.h>
#include <linux/mm_types.h>
#include <linux/mmdebug.h>
#include <linux/fs.h>
@ -196,6 +197,11 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
* huge_pte_offset(): Walk the hugetlb pgtable until the last level PTE.
* Returns the pte_t* if found, or NULL if the address is not mapped.
*
* IMPORTANT: we should normally not directly call this function, instead
* this is only a common interface to implement arch-specific
* walker. Please use hugetlb_walk() instead, because that will attempt to
* verify the locking for you.
*
* Since this function will walk all the pgtable pages (including not only
* high-level pgtable page, but also PUD entry that can be unshared
* concurrently for VM_SHARED), the caller of this function should be
@ -1229,4 +1235,35 @@ bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr);
#define flush_hugetlb_tlb_range(vma, addr, end) flush_tlb_range(vma, addr, end)
#endif
static inline bool __vma_shareable_lock(struct vm_area_struct *vma)
{
return (vma->vm_flags & VM_MAYSHARE) && vma->vm_private_data;
}
/*
* Safe version of huge_pte_offset() to check the locks. See comments
* above huge_pte_offset().
*/
static inline pte_t *
hugetlb_walk(struct vm_area_struct *vma, unsigned long addr, unsigned long sz)
{
#if defined(CONFIG_HUGETLB_PAGE) && \
defined(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) && defined(CONFIG_LOCKDEP)
struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
/*
* If pmd sharing possible, locking needed to safely walk the
* hugetlb pgtables. More information can be found at the comment
* above huge_pte_offset() in the same file.
*
* NOTE: lockdep_is_held() is only defined with CONFIG_LOCKDEP.
*/
if (__vma_shareable_lock(vma))
WARN_ON_ONCE(!lockdep_is_held(&vma_lock->rw_sema) &&
!lockdep_is_held(
&vma->vm_file->f_mapping->i_mmap_rwsem));
#endif
return huge_pte_offset(vma->vm_mm, addr, sz);
}
#endif /* _LINUX_HUGETLB_H */

31
mm/hugetlb.c
View File

@ -260,11 +260,6 @@ static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
/*
* hugetlb vma_lock helper routines
*/
static bool __vma_shareable_lock(struct vm_area_struct *vma)
{
return vma->vm_flags & VM_MAYSHARE && vma->vm_private_data;
}
void hugetlb_vma_lock_read(struct vm_area_struct *vma)
{
if (__vma_shareable_lock(vma)) {
@ -4980,7 +4975,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
} else {
/*
* For shared mappings the vma lock must be held before
* calling huge_pte_offset in the src vma. Otherwise, the
* calling hugetlb_walk() in the src vma. Otherwise, the
* returned ptep could go away if part of a shared pmd and
* another thread calls huge_pmd_unshare.
*/
@ -4990,7 +4985,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
last_addr_mask = hugetlb_mask_last_page(h);
for (addr = src_vma->vm_start; addr < src_vma->vm_end; addr += sz) {
spinlock_t *src_ptl, *dst_ptl;
src_pte = huge_pte_offset(src, addr, sz);
src_pte = hugetlb_walk(src_vma, addr, sz);
if (!src_pte) {
addr |= last_addr_mask;
continue;
@ -5197,7 +5192,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma,
hugetlb_vma_lock_write(vma);
i_mmap_lock_write(mapping);
for (; old_addr < old_end; old_addr += sz, new_addr += sz) {
src_pte = huge_pte_offset(mm, old_addr, sz);
src_pte = hugetlb_walk(vma, old_addr, sz);
if (!src_pte) {
old_addr |= last_addr_mask;
new_addr |= last_addr_mask;
@ -5260,7 +5255,7 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
last_addr_mask = hugetlb_mask_last_page(h);
address = start;
for (; address < end; address += sz) {
ptep = huge_pte_offset(mm, address, sz);
ptep = hugetlb_walk(vma, address, sz);
if (!ptep) {
address |= last_addr_mask;
continue;
@ -5573,7 +5568,7 @@ retry_avoidcopy:
mutex_lock(&hugetlb_fault_mutex_table[hash]);
hugetlb_vma_lock_read(vma);
spin_lock(ptl);
ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
ptep = hugetlb_walk(vma, haddr, huge_page_size(h));
if (likely(ptep &&
pte_same(huge_ptep_get(ptep), pte)))
goto retry_avoidcopy;
@ -5611,7 +5606,7 @@ retry_avoidcopy:
* before the page tables are altered
*/
spin_lock(ptl);
ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
ptep = hugetlb_walk(vma, haddr, huge_page_size(h));
if (likely(ptep && pte_same(huge_ptep_get(ptep), pte))) {
/* Break COW or unshare */
huge_ptep_clear_flush(vma, haddr, ptep);
@ -6397,7 +6392,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
return NULL;
hugetlb_vma_lock_read(vma);
pte = huge_pte_offset(mm, haddr, huge_page_size(h));
pte = hugetlb_walk(vma, haddr, huge_page_size(h));
if (!pte)
goto out_unlock;
@ -6462,8 +6457,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
*
* Note that page table lock is not held when pte is null.
*/
pte = huge_pte_offset(mm, vaddr & huge_page_mask(h),
huge_page_size(h));
pte = hugetlb_walk(vma, vaddr & huge_page_mask(h),
huge_page_size(h));
if (pte)
ptl = huge_pte_lock(h, mm, pte);
absent = !pte || huge_pte_none(huge_ptep_get(pte));
@ -6654,7 +6649,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
last_addr_mask = hugetlb_mask_last_page(h);
for (; address < end; address += psize) {
spinlock_t *ptl;
ptep = huge_pte_offset(mm, address, psize);
ptep = hugetlb_walk(vma, address, psize);
if (!ptep) {
if (!uffd_wp) {
address |= last_addr_mask;
@ -7064,8 +7059,8 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
saddr = page_table_shareable(svma, vma, addr, idx);
if (saddr) {
spte = huge_pte_offset(svma->vm_mm, saddr,
vma_mmu_pagesize(svma));
spte = hugetlb_walk(svma, saddr,
vma_mmu_pagesize(svma));
if (spte) {
get_page(virt_to_page(spte));
break;
@ -7377,7 +7372,7 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
hugetlb_vma_lock_write(vma);
i_mmap_lock_write(vma->vm_file->f_mapping);
for (address = start; address < end; address += PUD_SIZE) {
ptep = huge_pte_offset(mm, address, sz);
ptep = hugetlb_walk(vma, address, sz);
if (!ptep)
continue;
ptl = huge_pte_lock(h, mm, ptep);

9
mm/page_vma_mapped.c
View File

@ -168,9 +168,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
/* The only possible mapping was handled on last iteration */
if (pvmw->pte)
return not_found(pvmw);
/* when pud is not present, pte will be NULL */
pvmw->pte = huge_pte_offset(mm, pvmw->address, size);
/*
* All callers that get here will already hold the
* i_mmap_rwsem. Therefore, no additional locks need to be
* taken before calling hugetlb_walk().
*/
pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
if (!pvmw->pte)
return false;

4
mm/pagewalk.c
View File

@ -305,13 +305,11 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end,
hugetlb_vma_lock_read(vma);
do {
next = hugetlb_entry_end(h, addr, end);
pte = huge_pte_offset(walk->mm, addr & hmask, sz);
pte = hugetlb_walk(vma, addr & hmask, sz);
if (pte)
err = ops->hugetlb_entry(pte, hmask, addr, next, walk);
else if (ops->pte_hole)
err = ops->pte_hole(addr, next, -1, walk);
if (err)
break;
} while (addr = next, addr != end);