linux-kernel - [PATCH v1 3/3] KVM: arm64: Using rcu_read_lock() for kvm_pgtable_stage2

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Message-ID: <20230608220558.39094-4-ctshao@google.com>
Date:   Thu,  8 Jun 2023 15:05:41 -0700
From:   Chun-Tse Shao <ctshao@...gle.com>
To:     linux-kernel@...r.kernel.org, yuzhao@...gle.com,
        oliver.upton@...ux.dev
Cc:     Chun-Tse Shao <ctshao@...gle.com>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ben Gardon <bgardon@...gle.com>,
        Gavin Shan <gshan@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev
Subject: [PATCH v1 3/3] KVM: arm64: Using rcu_read_lock() for kvm_pgtable_stage2_mkyoung()

Access bit is RCU safe and can be set without taking kvm->mmu_lock().
Replacing existing kvm->mmu_lock() with rcu_read_lock() for better
performance.

Original disussion can be found in:
https://lore.kernel.org/kvmarm/CAOUHufZrfnfcbrqSzmHkejR5MA2gmGKZ3LMRhbLHV+1427z=Tw@mail.gmail.com/

Suggested-by: Yu Zhao <yuzhao@...gle.com>
Signed-off-by: Chun-Tse Shao <ctshao@...gle.com>
---
 arch/arm64/kvm/mmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 3b9d4d24c361..0f7ea66fb894 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1437,10 +1437,10 @@ static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
 
 	trace_kvm_access_fault(fault_ipa);
 
-	read_lock(&vcpu->kvm->mmu_lock);
+	rcu_read_lock();
 	mmu = vcpu->arch.hw_mmu;
 	pte = kvm_pgtable_stage2_mkyoung(mmu->pgt, fault_ipa);
-	read_unlock(&vcpu->kvm->mmu_lock);
+	rcu_read_unlock();
 
 	if (kvm_pte_valid(pte))
 		kvm_set_pfn_accessed(kvm_pte_to_pfn(pte));
-- 
2.41.0.162.gfafddb0af9-goog