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authorWill Deacon <will.deacon@arm.com>2016-06-07 17:55:15 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-06-24 10:18:19 -0700
commit5e8b53a4db947494f1d808469a411f7f2f8bb3ca (patch)
treef8e22db5c604427f82b297436049276204a715ab
parentd0bc1f47b8a7eee50b10035c645f6e6d7e719a62 (diff)
arm64: mm: always take dirty state from new pte in ptep_set_access_flags
commit 0106d456c4cb1770253fefc0ab23c9ca760b43f7 upstream. 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. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-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 40f5522245a2..4c1a118c1d09 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;
/*