On 08/13/2018 10:40 AM, Punit Agrawal wrote:

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") Change-Id: I28e17daf394a4821b13c2cf8726bf72bf30434f9 Signed-off-by: Punit Agrawal punit.agrawal@arm.com Cc: Marc Zyngier marc.zyngier@arm.com Cc: Christoffer Dall christoffer.dall@arm.com Cc: Suzuki Poulose suzuki.poulose@arm.com Cc: stable@vger.kernel.org

---

virt/kvm/arm/mmu.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c index 2ab977edc63c..d0a9dccc3793 100644 --- a/virt/kvm/arm/mmu.c +++ b/virt/kvm/arm/mmu.c @@ -1120,6 +1120,10 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache, /* 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))
  

• 	goto out;
  

• kvm_set_pte(pte, __pte(0)); kvm_tlb_flush_vmid_ipa(kvm, addr); } else {

@@ -1127,6 +1131,7 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache, } kvm_set_pte(pte, *new_pte); +out:

Similar comments as the previous patch, either way:

Reviewed-by: Suzuki K Poulose suzuki.poulose@arm.com