From: Oliver Upton <oliver.upton@linux.dev>
To: Chun-Tse Shao <ctshao@google.com>
Cc: linux-kernel@vger.kernel.org, yuzhao@google.com,
Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Ben Gardon <bgardon@google.com>,
Gavin Shan <gshan@redhat.com>,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH v1 3/3] KVM: arm64: Using rcu_read_lock() for kvm_pgtable_stage2_mkyoung()
Date: Fri, 9 Jun 2023 14:51:09 +0000 [thread overview]
Message-ID: <ZIM8XccN31XSb+Qh@linux.dev> (raw)
In-Reply-To: <20230608220558.39094-4-ctshao@google.com>
On Thu, Jun 08, 2023 at 03:05:41PM -0700, Chun-Tse Shao wrote:
> 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();
What is the point of acquiring the RCU read lock here?
kvm_pgtable_walk_{begin,end}() already do the exact same for any
'shared' walk.
I agree with Marc that this warrants some very clear benchmark data
showing the value of the change. As I had mentioned to Yu, I already
implemented this for my own purposes, but wasn't able to see a
significant improvement over acquiring the MMU lock for read.
--
Thanks,
Oliver
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next prev parent reply other threads:[~2023-06-09 14:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-08 22:05 [PATCH v1 1/3] KVM: arm64: Consistently use free_removed_table() for stage-2 Chun-Tse Shao
2023-06-08 22:05 ` [PATCH v1 2/3] KVM: arm64: Only initiate walk if page_count() > 1 in free_removed_table() Chun-Tse Shao
2023-06-08 22:05 ` [PATCH v1 3/3] KVM: arm64: Using rcu_read_lock() for kvm_pgtable_stage2_mkyoung() Chun-Tse Shao
2023-06-09 7:44 ` Marc Zyngier
2023-06-09 22:58 ` Chun-Tse Shao
2023-06-09 14:51 ` Oliver Upton [this message]
2023-06-08 22:13 ` [PATCH v1 1/3] KVM: arm64: Consistently use free_removed_table() for stage-2 Yu Zhao
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