linux-kernel - [PATCH v2 5/6] KVM: arm64: Handle access faults behind the read lock

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Message-Id: <20221202185156.696189-6-oliver.upton@linux.dev>
Date:   Fri,  2 Dec 2022 18:51:55 +0000
From:   Oliver Upton <oliver.upton@...ux.dev>
To:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
        Ricardo Koller <ricarkol@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 5/6] KVM: arm64: Handle access faults behind the read lock

As the underlying software walkers are able to traverse and update
stage-2 in parallel there is no need to serialize access faults.

Only take the read lock when handling an access fault.

Signed-off-by: Oliver Upton <oliver.upton@...ux.dev>
---
 arch/arm64/kvm/hyp/pgtable.c | 3 ++-
 arch/arm64/kvm/mmu.c         | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index aa36d896bd8c..30575b5f5dcd 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1120,7 +1120,8 @@ kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr)
 
 	ret = stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0,
 				       &pte, NULL,
-				       KVM_PGTABLE_WALK_HANDLE_FAULT);
+				       KVM_PGTABLE_WALK_HANDLE_FAULT |
+				       KVM_PGTABLE_WALK_SHARED);
 	if (!ret)
 		dsb(ishst);
 
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index dd8c715f0775..25e18e1d9a15 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1406,10 +1406,10 @@ static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
 
 	trace_kvm_access_fault(fault_ipa);
 
-	write_lock(&vcpu->kvm->mmu_lock);
+	read_lock(&vcpu->kvm->mmu_lock);
 	mmu = vcpu->arch.hw_mmu;
 	pte = kvm_pgtable_stage2_mkyoung(mmu->pgt, fault_ipa);
-	write_unlock(&vcpu->kvm->mmu_lock);
+	read_unlock(&vcpu->kvm->mmu_lock);
 
 	if (kvm_pte_valid(pte))
 		kvm_set_pfn_accessed(kvm_pte_to_pfn(pte));
-- 
2.39.0.rc0.267.gcb52ba06e7-goog