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([2001:b07:6468:f312:9af8:e5f5:7516:fa89]) by smtp.googlemail.com with ESMTPSA id p17-20020a50cd91000000b004479cec6496sm1102859edi.75.2022.08.26.03.58.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 26 Aug 2022 03:58:27 -0700 (PDT) Message-ID: <99364855-b4e9-8a69-e1ca-ed09d103e4c8@redhat.com> Date: Fri, 26 Aug 2022 12:58:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Content-Language: en-US To: Marc Zyngier , Oliver Upton Cc: Gavin Shan , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, peterx@redhat.com, corbet@lwn.net, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, shuah@kernel.org, seanjc@google.com, drjones@redhat.com, dmatlack@google.com, bgardon@google.com, ricarkol@google.com, zhenyzha@redhat.com, shan.gavin@gmail.com References: <20220819005601.198436-1-gshan@redhat.com> <20220819005601.198436-2-gshan@redhat.com> <87lerkwtm5.wl-maz@kernel.org> <41fb5a1f-29a9-e6bb-9fab-4c83a2a8fce5@redhat.com> <87fshovtu0.wl-maz@kernel.org> <87a67uwve8.wl-maz@kernel.org> From: Paolo Bonzini Subject: Re: [PATCH v1 1/5] KVM: arm64: Enable ring-based dirty memory tracking In-Reply-To: <87a67uwve8.wl-maz@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 8/23/22 22:35, Marc Zyngier wrote: >> Heh, yeah I need to get that out the door. I'll also note that Gavin's >> changes are still relevant without that series, as we do write unprotect >> in parallel at PTE granularity after commit f783ef1c0e82 ("KVM: arm64: >> Add fast path to handle permission relaxation during dirty logging"). > > Ah, true. Now if only someone could explain how the whole > producer-consumer thing works without a trace of a barrier, that'd be > great... Do you mean this? void kvm_dirty_ring_push(struct kvm_dirty_ring *ring, u32 slot, u64 offset) { struct kvm_dirty_gfn *entry; /* It should never get full */ WARN_ON_ONCE(kvm_dirty_ring_full(ring)); entry = &ring->dirty_gfns[ring->dirty_index & (ring->size - 1)]; entry->slot = slot; entry->offset = offset; /* * Make sure the data is filled in before we publish this to * the userspace program. There's no paired kernel-side reader. */ smp_wmb(); kvm_dirty_gfn_set_dirtied(entry); ring->dirty_index++; trace_kvm_dirty_ring_push(ring, slot, offset); } The matching smp_rmb() is in userspace. Paolo