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authorWill Deacon2017-12-12 10:48:54 +0000
committerWill Deacon2017-12-12 11:42:24 +0000
commit86c9e8126e9fbcbf06c36e285168b880369a537c (patch)
tree91889a0eaf4e732fa83a17f9d9e55c192c25574a /arch/arm64
parent8781bcbc5e69d7da69e84c7044ca0284848d5d01 (diff)
arm64: mm: Fix false positives in set_pte_at access/dirty race detection
Jiankang reports that our race detection in set_pte_at is firing when copying the page tables in dup_mmap as a result of a fork(). In this situation, the page table isn't actually live and so there is no way that we can race with a concurrent update from the hardware page table walker. This patch reworks the race detection so that we require either the mm to match the current active_mm (i.e. currently installed in our TTBR0) or the mm_users count to be greater than 1, implying that the page table could be live in another CPU. The mm_users check might still be racy, but we'll avoid false positives and it's not realistic to validate that all the necessary locks are held as part of this assertion. Cc: Yisheng Xie <xieyisheng1@huawei.com> Reported-by: Jiankang Chen <chenjiankang1@huawei.com> Tested-by: Jiankang Chen <chenjiankang1@huawei.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64')
-rw-r--r--arch/arm64/include/asm/pgtable.h8
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 3ff03a755c32..bdcc7f1c9d06 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -42,6 +42,8 @@
#include <asm/cmpxchg.h>
#include <asm/fixmap.h>
#include <linux/mmdebug.h>
+#include <linux/mm_types.h>
+#include <linux/sched.h>
extern void __pte_error(const char *file, int line, unsigned long val);
extern void __pmd_error(const char *file, int line, unsigned long val);
@@ -215,9 +217,6 @@ static inline void set_pte(pte_t *ptep, pte_t pte)
}
}
-struct mm_struct;
-struct vm_area_struct;
-
extern void __sync_icache_dcache(pte_t pteval, unsigned long addr);
/*
@@ -246,7 +245,8 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
* hardware updates of the pte (ptep_set_access_flags safely changes
* valid ptes without going through an invalid entry).
*/
- if (pte_valid(*ptep) && pte_valid(pte)) {
+ if (IS_ENABLED(CONFIG_DEBUG_VM) && pte_valid(*ptep) && pte_valid(pte) &&
+ (mm == current->active_mm || atomic_read(&mm->mm_users) > 1)) {
VM_WARN_ONCE(!pte_young(pte),
"%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
__func__, pte_val(*ptep), pte_val(pte));