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Date: Sat, 3 Jul 2021 10:30:18 +1000
From: Gavin Shan <gshan@...hat.com>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, anshuman.khandual@....com,
catalin.marinas@....com, will@...nel.org,
akpm@...ux-foundation.org, shan.gavin@...il.com
Subject: Re: [PATCH] mm/debug_vm_pgtable: Fix corrupted PG_arch_1 by
set_pmd_at()
On 7/2/21 8:32 PM, Gavin Shan wrote:
> There are two addresses selected: random virtual address and physical
> address corresponding to kernel symbol @start_kernel. During the PMD
> tests in pmd_advanced_tests(), the physical address is aligned down
> to the starting address of the huge page, whose size is 512MB on ARM64
> when we have 64KB base page size. After that, set_pmd_at() is called
> to populate the PMD entry. PG_arch_1, PG_dcache_clean on ARM64, is
> set to the page flags. Unforunately, the page, corresponding to the
> starting address of the huge page could be owned by buddy. It means
> PG_arch_1 can be unconditionally set to page owned by buddy.
>
> Afterwards, the page with PG_arch_1 set is fetched from buddy's free
> area list, but fails the checking. It leads to the following warning
> on ARM64:
>
> 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 calling flush_dcache_page() after each call
> to set_{pud, pmd, pte}_at() because PG_arch_1 isn't needed in any case.
>
> Fixes: a5c3b9ffb0f4 ("mm/debug_vm_pgtable: add tests validating advanced arch page table helpers")
> Cc: stable@...r.kernel.org # v5.9+
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
> mm/debug_vm_pgtable.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 92bfc37300df..7dedf6c6dd25 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>
>
> @@ -91,6 +93,7 @@ static void __init pte_advanced_tests(struct mm_struct *mm,
> unsigned long pfn, unsigned long vaddr,
> pgprot_t prot)
> {
> + struct page *page = pfn_to_page(pfn);
> pte_t pte = pfn_pte(pfn, prot);
>
> /*
> @@ -102,6 +105,7 @@ static void __init pte_advanced_tests(struct mm_struct *mm,
> pr_debug("Validating PTE advanced\n");
> pte = pfn_pte(pfn, prot);
> set_pte_at(mm, vaddr, ptep, pte);
> + flush_dcache_page(page);
> ptep_set_wrprotect(mm, vaddr, ptep);
> pte = ptep_get(ptep);
> WARN_ON(pte_write(pte));
> @@ -113,6 +117,7 @@ static void __init pte_advanced_tests(struct mm_struct *mm,
> pte = pte_wrprotect(pte);
> pte = pte_mkclean(pte);
> set_pte_at(mm, vaddr, ptep, pte);
> + flush_dcache_page(page);
> pte = pte_mkwrite(pte);
> pte = pte_mkdirty(pte);
> ptep_set_access_flags(vma, vaddr, ptep, pte, 1);
> @@ -125,6 +130,7 @@ static void __init pte_advanced_tests(struct mm_struct *mm,
> pte = pfn_pte(pfn, prot);
> pte = pte_mkyoung(pte);
> set_pte_at(mm, vaddr, ptep, pte);
> + flush_dcache_page(page);
> ptep_test_and_clear_young(vma, vaddr, ptep);
> pte = ptep_get(ptep);
> WARN_ON(pte_young(pte));
> @@ -186,6 +192,7 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
> unsigned long pfn, unsigned long vaddr,
> pgprot_t prot, pgtable_t pgtable)
> {
> + struct page *page = pfn_to_page(pfn);
> pmd_t pmd;
>
> if (!has_transparent_hugepage())
> @@ -199,6 +206,7 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
>
> pmd = pfn_pmd(pfn, prot);
> set_pmd_at(mm, vaddr, pmdp, pmd);
> + flush_dcache_page(page);
> pmdp_set_wrprotect(mm, vaddr, pmdp);
> pmd = READ_ONCE(*pmdp);
> WARN_ON(pmd_write(pmd));
> @@ -210,6 +218,7 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
> pmd = pmd_wrprotect(pmd);
> pmd = pmd_mkclean(pmd);
> set_pmd_at(mm, vaddr, pmdp, pmd);
> + flush_dcache_page(page);
> pmd = pmd_mkwrite(pmd);
> pmd = pmd_mkdirty(pmd);
> pmdp_set_access_flags(vma, vaddr, pmdp, pmd, 1);
> @@ -222,6 +231,7 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
> pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
> pmd = pmd_mkyoung(pmd);
> set_pmd_at(mm, vaddr, pmdp, pmd);
> + flush_dcache_page(page);
> pmdp_test_and_clear_young(vma, vaddr, pmdp);
> pmd = READ_ONCE(*pmdp);
> WARN_ON(pmd_young(pmd));
> @@ -334,6 +344,7 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
> unsigned long pfn, unsigned long vaddr,
> pgprot_t prot)
> {
> + struct page *page = pfn_to_page(page);
> pud_t pud;
>
Typo here. @page should be replaced by @pfn. I'm holding to post v2 until I
receive comments on v1.
> if (!has_transparent_hugepage())
> @@ -345,6 +356,7 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
>
> pud = pfn_pud(pfn, prot);
> set_pud_at(mm, vaddr, pudp, pud);
> + flush_dcache_page(page);
> pudp_set_wrprotect(mm, vaddr, pudp);
> pud = READ_ONCE(*pudp);
> WARN_ON(pud_write(pud));
> @@ -358,6 +370,7 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
> pud = pud_wrprotect(pud);
> pud = pud_mkclean(pud);
> set_pud_at(mm, vaddr, pudp, pud);
> + flush_dcache_page(page);
> pud = pud_mkwrite(pud);
> pud = pud_mkdirty(pud);
> pudp_set_access_flags(vma, vaddr, pudp, pud, 1);
> @@ -373,6 +386,7 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
> pud = pfn_pud(pfn, prot);
> pud = pud_mkyoung(pud);
> set_pud_at(mm, vaddr, pudp, pud);
> + flush_dcache_page(page);
> pudp_test_and_clear_young(vma, vaddr, pudp);
> pud = READ_ONCE(*pudp);
> WARN_ON(pud_young(pud));
> @@ -604,6 +618,7 @@ static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
> unsigned long pfn, unsigned long vaddr,
> pgprot_t prot)
> {
> + struct page *page = pfn_to_page(pfn);
> pte_t pte = pfn_pte(pfn, prot);
>
> pr_debug("Validating PTE clear\n");
> @@ -611,6 +626,7 @@ static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
> pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
> #endif
> set_pte_at(mm, vaddr, ptep, pte);
> + flush_dcache_page(page);
> barrier();
> pte_clear(mm, vaddr, ptep);
> pte = ptep_get(ptep);
>
Thanks,
Gavin
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