From 86c9e8126e9fbcbf06c36e285168b880369a537c Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 12 Dec 2017 10:48:54 +0000 Subject: [PATCH] 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 Reported-by: Jiankang Chen Tested-by: Jiankang Chen Signed-off-by: Will Deacon --- arch/arm64/include/asm/pgtable.h | 8 ++++---- 1 file 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 #include #include +#include +#include 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)); -- 2.11.0