linux-kernel - Re: [PATCH 3/4] KVM: arm64: Handle access faults behind the read lock

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Message-ID: <Y4Zy/MtIgeLyRGy9@google.com>
Date:   Tue, 29 Nov 2022 13:00:44 -0800
From:   Ricardo Koller <ricarkol@...gle.com>
To:     Oliver Upton <oliver.upton@...ux.dev>
Cc:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: arm64: Handle access faults behind the read lock

On Tue, Nov 29, 2022 at 07:19:45PM +0000, Oliver Upton wrote:
> 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 | 2 +-
>  arch/arm64/kvm/mmu.c         | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 9626f615d9b8..1a3dd9774707 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1097,7 +1097,7 @@ kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr)
>  	int ret;
>  
>  	ret = stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0,
> -				       &pte, NULL, 0);
> +				       &pte, NULL, KVM_PGTABLE_WALK_SHARED);
>  	if (!ret)
>  		dsb(ishst);
>  
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 886ad5ee767a..347985a56414 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1404,10 +1404,10 @@ 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));
> -- 
> 2.38.1.584.g0f3c55d4c2-goog
> 
> _______________________________________________
> kvmarm mailing list
> kvmarm@...ts.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

Reviewed-by: Ricardo Koller <ricarkol@...gle.com>

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