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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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240531_121825_727079_F695179D X-CRM114-Status: GOOD ( 19.49 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, May 31, 2024 at 12:11:33PM -0700, Oliver Upton wrote: > 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. Oh, and the WARN_ON() in kvm_pgtable_stage2_test_clear_young() is bogus now. Maybe demote it to: r = kvm_pgtable_walk(...); WARN_ON_ONCE(r && r != -EAGAIN); -- Thanks, Oliver _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel