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From: Oliver Upton To: James Houghton Cc: Andrew Morton , Paolo Bonzini , Albert Ou , Ankit Agrawal , Anup Patel , Atish Patra , Axel Rasmussen , Bibo Mao , Catalin Marinas , David Matlack , David Rientjes , Huacai Chen , James Morse , Jonathan Corbet , Marc Zyngier , Michael Ellerman , Nicholas Piggin , Palmer Dabbelt , Paul Walmsley , Raghavendra Rao Ananta , Ryan Roberts , Sean Christopherson , Shaoqin Huang , Shuah Khan , Suzuki K Poulose , Tianrui Zhao , Will Deacon , Yu Zhao , Zenghui Yu , kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev Subject: Re: [PATCH v4 6/7] KVM: arm64: Relax locking for kvm_test_age_gfn and kvm_age_gfn Message-ID: References: <20240529180510.2295118-1-jthoughton@google.com> <20240529180510.2295118-7-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-mips@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240529180510.2295118-7-jthoughton@google.com> X-Migadu-Flow: FLOW_OUT On Wed, May 29, 2024 at 06:05:09PM +0000, James Houghton wrote: [...] > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index 9e2bbee77491..eabb07c66a07 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -1319,10 +1319,8 @@ static int stage2_age_walker(const struct kvm_pgtable_visit_ctx *ctx, > data->young = true; > > /* > - * stage2_age_walker() is always called while holding the MMU lock for > - * write, so this will always succeed. Nonetheless, this deliberately > - * follows the race detection pattern of the other stage-2 walkers in > - * case the locking mechanics of the MMU notifiers is ever changed. > + * This walk may not be exclusive; the PTE is permitted to change > + * from under us. > */ > if (data->mkold && !stage2_try_set_pte(ctx, new)) > return -EAGAIN; It is probably worth mentioning that if there was a race to update the PTE then the GFN is most likely young, so failing to clear AF probably isn't even consequential. -- Thanks, Oliver