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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id f16-20020aa78b10000000b0050a81508653sm12251481pfd.198.2022.04.25.11.16.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Apr 2022 11:16:56 -0700 (PDT) Date: Mon, 25 Apr 2022 18:16:52 +0000 From: Sean Christopherson To: Oliver Upton Subject: Re: [RFC PATCH 06/17] KVM: arm64: Implement break-before-make sequence for parallel walks Message-ID: References: <20220415215901.1737897-1-oupton@google.com> <20220415215901.1737897-7-oupton@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Cc: kvm@vger.kernel.org, Marc Zyngier , Peter Shier , Ben Gardon , David Matlack , Paolo Bonzini , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Mon, Apr 25, 2022, Oliver Upton wrote: > On Mon, Apr 25, 2022 at 8:13 AM Sean Christopherson wrote: > > > > On Fri, Apr 15, 2022, Oliver Upton wrote: > > > The ARM architecture requires that software use the 'break-before-make' > > > sequence whenever memory is being remapped. > > > > What does "remapped" mean here? Changing the pfn? Promoting/demoting to/from a > > huge page? > > Both, but in the case of this series it is mostly concerned with > promotion/demotion. I'll make this language a bit more precise next > time around. Please be very precise :-) It matters because it should be impossible for KVM to actually change a PFN in a valid PTE. Callers of mmu_notifier_change_pte() are required to bookend it with mmu_notifier_invalidate_range_start/end(), i.e. KVM should have zapped all PTEs and should not establish new PTEs. I'd actually like to drop mmu_notifier_change_pte() altogether, because for all intents and purposes, it's dead code. But convincing "everyone" that dropping it instead of trying to salvage it for KSM is too much work :-) _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm