From: Punit Agrawal <punit.agrawal@arm.com>
To: kvmarm@lists.cs.columbia.edu
Cc: Punit Agrawal <punit.agrawal@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, suzuki.poulose@arm.com,
marc.zyngier@arm.com, christoffer.dall@arm.com,
stable@vger.kernel.org
Subject: [PATCH v2 2/2] KVM: arm/arm64: Skip updating PTE entry if no change
Date: Mon, 13 Aug 2018 10:40:49 +0100 [thread overview]
Message-ID: <20180813094049.3726-3-punit.agrawal@arm.com> (raw)
In-Reply-To: <20180813094049.3726-1-punit.agrawal@arm.com>
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:
return 0;
}
--
2.18.0
next prev parent reply other threads:[~2018-08-13 9:41 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-13 9:40 [PATCH v2 0/2] KVM: Fix refaulting due to page table update Punit Agrawal
2018-08-13 9:40 ` [PATCH v2 1/2] KVM: arm/arm64: Skip updating PMD entry if no change Punit Agrawal
2018-08-13 9:46 ` Suzuki K Poulose
2018-08-13 10:01 ` Punit Agrawal
2018-08-13 10:11 ` Marc Zyngier
2018-08-13 10:18 ` Punit Agrawal
2018-08-13 9:40 ` Punit Agrawal [this message]
2018-08-13 9:47 ` [PATCH v2 2/2] KVM: arm/arm64: Skip updating PTE " Suzuki K Poulose
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