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    SubjectRe: [PATCH v4 12/12] mm/debug_vm_pgtable: Fix corrupted page flag
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    On 7/27/21 11:44 AM, Gavin Shan wrote:
    > In page table entry modifying tests, set_xxx_at() are used to populate
    > the page table entries. On ARM64, PG_arch_1 (PG_dcache_clean) flag is
    > set to the target page flag if execution permission is given. The logic
    > exits since commit 4f04d8f00545 ("arm64: MMU definitions"). The page
    > flag is kept when the page is free'd to buddy's free area list. However,
    > it will trigger page checking failure when it's pulled from the buddy's
    > free area list, as the following warning messages indicate.
    >
    > BUG: Bad page state in process memhog pfn:08000
    > page:0000000015c0a628 refcount:0 mapcount:0 \
    > mapping:0000000000000000 index:0x1 pfn:0x8000
    > flags: 0x7ffff8000000800(arch_1|node=0|zone=0|lastcpupid=0xfffff)
    > raw: 07ffff8000000800 dead000000000100 dead000000000122 0000000000000000
    > raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
    > page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag(s) set
    >
    > This fixes the issue by clearing PG_arch_1 through flush_dcache_page()
    > after set_xxx_at() is called. For architectures other than ARM64, the
    > unexpected overhead of cache flushing is acceptable.
    >
    > Signed-off-by: Gavin Shan <gshan@redhat.com>
    > ---
    > mm/debug_vm_pgtable.c | 55 +++++++++++++++++++++++++++++++++++++++----
    > 1 file changed, 51 insertions(+), 4 deletions(-)
    >
    > diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
    > index 162ff6329f7b..d2c2d23e542e 100644
    > --- a/mm/debug_vm_pgtable.c
    > +++ b/mm/debug_vm_pgtable.c
    > @@ -29,6 +29,8 @@
    > #include <linux/start_kernel.h>
    > #include <linux/sched/mm.h>
    > #include <linux/io.h>
    > +
    > +#include <asm/cacheflush.h>
    > #include <asm/pgalloc.h>
    > #include <asm/tlbflush.h>
    >
    > @@ -119,19 +121,28 @@ static void __init pte_basic_tests(struct pgtable_debug_args *args, int idx)
    >
    > static void __init pte_advanced_tests(struct pgtable_debug_args *args)
    > {
    > + struct page *page;
    > pte_t pte;
    >
    > /*
    > * Architectures optimize set_pte_at by avoiding TLB flush.
    > * This requires set_pte_at to be not used to update an
    > * existing pte entry. Clear pte before we do set_pte_at
    > + *
    > + * flush_dcache_page() is called after set_pte_at() to clear
    > + * PG_arch_1 for the page on ARM64. The page flag isn't cleared
    > + * when it's released and page allocation check will fail when
    > + * the page is allocated again. For architectures other than ARM64,
    > + * the unexpected overhead of cache flushing is acceptable.
    > */
    > - if (args->pte_pfn == ULONG_MAX)
    > + page = (args->pte_pfn != ULONG_MAX) ? pfn_to_page(args->pte_pfn) : NULL;
    > + if (!page)
    > return;
    >
    > pr_debug("Validating PTE advanced\n");
    > pte = pfn_pte(args->pte_pfn, args->page_prot);
    > set_pte_at(args->mm, args->vaddr, args->ptep, pte);
    > + flush_dcache_page(page);
    > ptep_set_wrprotect(args->mm, args->vaddr, args->ptep);
    > pte = ptep_get(args->ptep);
    > WARN_ON(pte_write(pte));
    > @@ -143,6 +154,7 @@ static void __init pte_advanced_tests(struct pgtable_debug_args *args)
    > pte = pte_wrprotect(pte);
    > pte = pte_mkclean(pte);
    > set_pte_at(args->mm, args->vaddr, args->ptep, pte);
    > + flush_dcache_page(page);
    > pte = pte_mkwrite(pte);
    > pte = pte_mkdirty(pte);
    > ptep_set_access_flags(args->vma, args->vaddr, args->ptep, pte, 1);
    > @@ -155,6 +167,7 @@ static void __init pte_advanced_tests(struct pgtable_debug_args *args)
    > pte = pfn_pte(args->pte_pfn, args->page_prot);
    > pte = pte_mkyoung(pte);
    > set_pte_at(args->mm, args->vaddr, args->ptep, pte);
    > + flush_dcache_page(page);
    > ptep_test_and_clear_young(args->vma, args->vaddr, args->ptep);
    > pte = ptep_get(args->ptep);
    > WARN_ON(pte_young(pte));
    > @@ -213,15 +226,24 @@ static void __init pmd_basic_tests(struct pgtable_debug_args *args, int idx)
    >
    > static void __init pmd_advanced_tests(struct pgtable_debug_args *args)
    > {
    > + struct page *page;
    > pmd_t pmd;
    > unsigned long vaddr = args->vaddr;
    >
    > if (!has_transparent_hugepage())
    > return;
    >
    > - if (args->pmd_pfn == ULONG_MAX)
    > + page = (args->pmd_pfn != ULONG_MAX) ? pfn_to_page(args->pmd_pfn) : NULL;
    > + if (!page)
    > return;
    >
    > + /*
    > + * flush_dcache_page() is called after set_pmd_at() to clear
    > + * PG_arch_1 for the page on ARM64. The page flag isn't cleared
    > + * when it's released and page allocation check will fail when
    > + * the page is allocated again. For architectures other than ARM64,
    > + * the unexpected overhead of cache flushing is acceptable.
    > + */
    > pr_debug("Validating PMD advanced\n");
    > /* Align the address wrt HPAGE_PMD_SIZE */
    > vaddr &= HPAGE_PMD_MASK;
    > @@ -230,6 +252,7 @@ static void __init pmd_advanced_tests(struct pgtable_debug_args *args)
    >
    > pmd = pfn_pmd(args->pmd_pfn, args->page_prot);
    > set_pmd_at(args->mm, vaddr, args->pmdp, pmd);
    > + flush_dcache_page(page);
    > pmdp_set_wrprotect(args->mm, vaddr, args->pmdp);
    > pmd = READ_ONCE(*args->pmdp);
    > WARN_ON(pmd_write(pmd));
    > @@ -241,6 +264,7 @@ static void __init pmd_advanced_tests(struct pgtable_debug_args *args)
    > pmd = pmd_wrprotect(pmd);
    > pmd = pmd_mkclean(pmd);
    > set_pmd_at(args->mm, vaddr, args->pmdp, pmd);
    > + flush_dcache_page(page);
    > pmd = pmd_mkwrite(pmd);
    > pmd = pmd_mkdirty(pmd);
    > pmdp_set_access_flags(args->vma, vaddr, args->pmdp, pmd, 1);
    > @@ -253,6 +277,7 @@ static void __init pmd_advanced_tests(struct pgtable_debug_args *args)
    > pmd = pmd_mkhuge(pfn_pmd(args->pmd_pfn, args->page_prot));
    > pmd = pmd_mkyoung(pmd);
    > set_pmd_at(args->mm, vaddr, args->pmdp, pmd);
    > + flush_dcache_page(page);
    > pmdp_test_and_clear_young(args->vma, vaddr, args->pmdp);
    > pmd = READ_ONCE(*args->pmdp);
    > WARN_ON(pmd_young(pmd));
    > @@ -339,21 +364,31 @@ static void __init pud_basic_tests(struct pgtable_debug_args *args, int idx)
    >
    > static void __init pud_advanced_tests(struct pgtable_debug_args *args)
    > {
    > + struct page *page;
    > unsigned long vaddr = args->vaddr;
    > pud_t pud;
    >
    > if (!has_transparent_hugepage())
    > return;
    >
    > - if (args->pud_pfn == ULONG_MAX)
    > + page = (args->pud_pfn != ULONG_MAX) ? pfn_to_page(args->pud_pfn) : NULL;
    > + if (!page)
    > return;
    >
    > + /*
    > + * flush_dcache_page() is called after set_pud_at() to clear
    > + * PG_arch_1 for the page on ARM64. The page flag isn't cleared
    > + * when it's released and page allocation check will fail when
    > + * the page is allocated again. For architectures other than ARM64,
    > + * the unexpected overhead of cache flushing is acceptable.
    > + */
    > pr_debug("Validating PUD advanced\n");
    > /* Align the address wrt HPAGE_PUD_SIZE */
    > vaddr &= HPAGE_PUD_MASK;
    >
    > pud = pfn_pud(args->pud_pfn, args->page_prot);
    > set_pud_at(args->mm, vaddr, args->pudp, pud);
    > + flush_dcache_page(page);
    > pudp_set_wrprotect(args->mm, vaddr, args->pudp);
    > pud = READ_ONCE(*args->pudp);
    > WARN_ON(pud_write(pud));
    > @@ -367,6 +402,7 @@ static void __init pud_advanced_tests(struct pgtable_debug_args *args)
    > pud = pud_wrprotect(pud);
    > pud = pud_mkclean(pud);
    > set_pud_at(args->mm, vaddr, args->pudp, pud);
    > + flush_dcache_page(page);
    > pud = pud_mkwrite(pud);
    > pud = pud_mkdirty(pud);
    > pudp_set_access_flags(args->vma, vaddr, args->pudp, pud, 1);
    > @@ -382,6 +418,7 @@ static void __init pud_advanced_tests(struct pgtable_debug_args *args)
    > pud = pfn_pud(args->pud_pfn, args->page_prot);
    > pud = pud_mkyoung(pud);
    > set_pud_at(args->mm, vaddr, args->pudp, pud);
    > + flush_dcache_page(page);
    > pudp_test_and_clear_young(args->vma, vaddr, args->pudp);
    > pud = READ_ONCE(*args->pudp);
    > WARN_ON(pud_young(pud));
    > @@ -594,16 +631,26 @@ static void __init pgd_populate_tests(struct pgtable_debug_args *args) { }
    >
    > static void __init pte_clear_tests(struct pgtable_debug_args *args)
    > {
    > + struct page *page;
    > pte_t pte = pfn_pte(args->pte_pfn, args->page_prot);
    >
    > - if (args->pte_pfn == ULONG_MAX)
    > + page = (args->pte_pfn != ULONG_MAX) ? pfn_to_page(args->pte_pfn) : NULL;
    > + if (!page)
    > return;
    >
    > + /*
    > + * flush_dcache_page() is called after set_pte_at() to clear
    > + * PG_arch_1 for the page on ARM64. The page flag isn't cleared
    > + * when it's released and page allocation check will fail when
    > + * the page is allocated again. For architectures other than ARM64,
    > + * the unexpected overhead of cache flushing is acceptable.
    > + */
    > pr_debug("Validating PTE clear\n");
    > #ifndef CONFIG_RISCV
    > pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
    > #endif
    > set_pte_at(args->mm, args->vaddr, args->ptep, pte);
    > + flush_dcache_page(page);
    > barrier();
    > pte_clear(args->mm, args->vaddr, args->ptep);
    > pte = ptep_get(args->ptep);
    >

    Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

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