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authorWill Deacon <will.deacon@arm.com>2016-06-07 17:55:15 +0100
committerWill Deacon <will.deacon@arm.com>2016-06-08 10:23:44 +0100
commit0106d456c4cb1770253fefc0ab23c9ca760b43f7 (patch)
tree9944baa248eb9db183c59bae7bd168c9af20bfab
parentaf8c34ce6ae32addda3788d54a7e340cad22516b (diff)
downloadlinux-0106d456c4cb1770253fefc0ab23c9ca760b43f7.tar.gz
arm64: mm: always take dirty state from new pte in ptep_set_access_flags
Commit 66dbd6e61a52 ("arm64: Implement ptep_set_access_flags() for hardware AF/DBM") ensured that pte flags are updated atomically in the face of potential concurrent, hardware-assisted updates. However, Alex reports that: | This patch breaks swapping for me. | In the broken case, you'll see either systemd cpu time spike (because | it's stuck in a page fault loop) or the system hang (because the | application owning the screen is stuck in a page fault loop). It turns out that this is because the 'dirty' argument to ptep_set_access_flags is always 0 for read faults, and so we can't use it to set PTE_RDONLY. The failing sequence is: 1. We put down a PTE_WRITE | PTE_DIRTY | PTE_AF pte 2. Memory pressure -> pte_mkold(pte) -> clear PTE_AF 3. A read faults due to the missing access flag 4. ptep_set_access_flags is called with dirty = 0, due to the read fault 5. pte is then made PTE_WRITE | PTE_DIRTY | PTE_AF | PTE_RDONLY (!) 6. A write faults, but pte_write is true so we get stuck The solution is to check the new page table entry (as would be done by the generic, non-atomic definition of ptep_set_access_flags that just calls set_pte_at) to establish the dirty state. Cc: <stable@vger.kernel.org> # 4.3+ Fixes: 66dbd6e61a52 ("arm64: Implement ptep_set_access_flags() for hardware AF/DBM") Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Reported-by: Alexander Graf <agraf@suse.de> Tested-by: Alexander Graf <agraf@suse.de> Signed-off-by: Will Deacon <will.deacon@arm.com>
-rw-r--r--arch/arm64/mm/fault.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 5954881a35ac..ba3fc12bd272 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -109,7 +109,7 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
* PTE_RDONLY is cleared by default in the asm below, so set it in
* back if necessary (read-only or clean PTE).
*/
- if (!pte_write(entry) || !dirty)
+ if (!pte_write(entry) || !pte_sw_dirty(entry))
pte_val(entry) |= PTE_RDONLY;
/*