Re: [PATCH] mm/debug_vm_pgtable: Fix corrupted PG_arch_1 by set_pmd_at()
From: Gavin Shan
Date: Fri Jul 02 2021 - 20:41:48 EST
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@xxxxxxxxxxxxxxx # v5.9+
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
---
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