[PATCH 3.16 134/328] KVM: arm/arm64: Skip updating PTE entry if no change

Ben Hutchings
2018-12-09T22:10:34Z

From: Punit Agrawal <punit.agrawal@arm.com>

commit 976d34e2dab10ece5ea8fe7090b7692913f89084 upstream.

When there is contention on faulting in a particular page table entry
at stage 2, the break-before-make requirement of the architecture can
lead to additional refaulting due to TLB invalidation.

Avoid this by skipping a page table update if the new value of the PTE
matches the previous value.

Fixes: d5d8184d35c9 ("KVM: ARM: Memory virtualization setup")
Reviewed-by: Suzuki Poulose <suzuki.poulose@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/arm/kvm/mmu.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -758,6 +758,10 @@ static int stage2_set_pte(struct kvm *kv
/* Create 2nd stage page table mapping - Level 3 */
old_pte = *pte;
if (pte_present(old_pte)) {
+ /* Skip page table update if there is no change */
+ if (pte_val(old_pte) == pte_val(*new_pte))
+ return 0;
+
kvm_set_pte(pte, __pte(0));
kvm_tlb_flush_vmid_ipa(kvm, addr);
} else {