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mm/mprotect: delete pmd_none_or_clear_bad_unless_trans_huge()

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change_pmd_range() had special pmd_none_or_clear_bad_unless_trans_huge(),
required to avoid "bad" choices when setting automatic NUMA hinting under
mmap_read_lock(); but most of that is already covered in pte_offset_map()
now.  change_pmd_range() just wants a pmd_none() check before wasting time
on MMU notifiers, then checks on the read-once _pmd value to work out
what's needed for huge cases.  If change_pte_range() returns -EAGAIN to
retry if pte_offset_map_lock() fails, nothing more special is needed.

Link: https://lkml.kernel.org/r/725a42a9-91e9-c868-925-e3a5fd40bb4f@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2023-06-08 18:30:48 -07:00 committed by Andrew Morton
parent 04dee9e85c
commit 670ddd8cdc
1 changed files with 17 additions and 57 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

74
mm/mprotect.c
View File

@ -93,22 +93,9 @@ static long change_pte_range(struct mmu_gather *tlb,
bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
tlb_change_page_size(tlb, PAGE_SIZE);
/*
* Can be called with only the mmap_lock for reading by
* prot_numa so we must check the pmd isn't constantly
* changing from under us from pmd_none to pmd_trans_huge
* and/or the other way around.
*/
if (pmd_trans_unstable(pmd))
return 0;
/*
* The pmd points to a regular pte so the pmd can't change
* from under us even if the mmap_lock is only hold for
* reading.
*/
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
if (!pte)
return -EAGAIN;
/* Get target node for single threaded private VMAs */
if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
@ -301,26 +288,6 @@ static long change_pte_range(struct mmu_gather *tlb,
return pages;
}
/*
* Used when setting automatic NUMA hinting protection where it is
* critical that a numa hinting PMD is not confused with a bad PMD.
*/
static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
{
pmd_t pmdval = pmdp_get_lockless(pmd);
if (pmd_none(pmdval))
return 1;
if (pmd_trans_huge(pmdval))
return 0;
if (unlikely(pmd_bad(pmdval))) {
pmd_clear_bad(pmd);
return 1;
}
return 0;
}
/*
* Return true if we want to split THPs into PTE mappings in change
* protection procedure, false otherwise.
@ -398,7 +365,8 @@ static inline long change_pmd_range(struct mmu_gather *tlb,
pmd = pmd_offset(pud, addr);
do {
long ret;
pmd_t _pmd;
again:
next = pmd_addr_end(addr, end);
ret = change_pmd_prepare(vma, pmd, cp_flags);
@ -406,16 +374,8 @@ static inline long change_pmd_range(struct mmu_gather *tlb,
pages = ret;
break;
}
/*
* Automatic NUMA balancing walks the tables with mmap_lock
* held for read. It's possible a parallel update to occur
* between pmd_trans_huge() and a pmd_none_or_clear_bad()
* check leading to a false positive and clearing.
* Hence, it's necessary to atomically read the PMD value
* for all the checks.
*/
if (!is_swap_pmd(*pmd) && !pmd_devmap(*pmd) &&
pmd_none_or_clear_bad_unless_trans_huge(pmd))
if (pmd_none(*pmd))
goto next;
/* invoke the mmu notifier if the pmd is populated */
@ -426,7 +386,8 @@ static inline long change_pmd_range(struct mmu_gather *tlb,
mmu_notifier_invalidate_range_start(&range);
}
if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
_pmd = pmdp_get_lockless(pmd);
if (is_swap_pmd(_pmd) || pmd_trans_huge(_pmd) || pmd_devmap(_pmd)) {
if ((next - addr != HPAGE_PMD_SIZE) ||
pgtable_split_needed(vma, cp_flags)) {
__split_huge_pmd(vma, pmd, addr, false, NULL);
@ -441,15 +402,10 @@ static inline long change_pmd_range(struct mmu_gather *tlb,
break;
}
} else {
/*
* change_huge_pmd() does not defer TLB flushes,
* so no need to propagate the tlb argument.
*/
int nr_ptes = change_huge_pmd(tlb, vma, pmd,
ret = change_huge_pmd(tlb, vma, pmd,
addr, newprot, cp_flags);
if (nr_ptes) {
if (nr_ptes == HPAGE_PMD_NR) {
if (ret) {
if (ret == HPAGE_PMD_NR) {
pages += HPAGE_PMD_NR;
nr_huge_updates++;
}
@ -460,8 +416,12 @@ static inline long change_pmd_range(struct mmu_gather *tlb,
}
/* fall through, the trans huge pmd just split */
}
pages += change_pte_range(tlb, vma, pmd, addr, next,
newprot, cp_flags);
ret = change_pte_range(tlb, vma, pmd, addr, next, newprot,
cp_flags);
if (ret < 0)
goto again;
pages += ret;
next:
cond_resched();
} while (pmd++, addr = next, addr != end);