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([2001:b07:6468:f312:8c9d:1a6f:4730:367c]) by smtp.gmail.com with ESMTPSA id b17sm17965088wru.36.2019.11.11.11.15.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2019 11:15:26 -0800 (PST) Subject: Re: [PATCH 1/2] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved To: Sean Christopherson , Dan Williams Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , KVM list , Linux Kernel Mailing List , Adam Borowski , David Hildenbrand References: <1cf71906-ba99-e637-650f-fc08ac4f3d5f@redhat.com> <20191106233913.GC21617@linux.intel.com> <0db7c328-1543-55db-bc02-c589deb3db22@redhat.com> <20191107155846.GA7760@linux.intel.com> <20191109014323.GB8254@linux.intel.com> <20191111182750.GE11805@linux.intel.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <707ce7d4-7149-f4c4-c150-801962a3197d@redhat.com> Date: Mon, 11 Nov 2019 20:15:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191111182750.GE11805@linux.intel.com> Content-Language: en-US X-MC-Unique: iJAPnOwNNAOn_9Fnph2LcQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/11/19 19:27, Sean Christopherson wrote: >> Thanks for this clarification. I do want to put out though that >> ZONE_DEVICE pages go idle, they don't get freed. As long as KVM drops >> its usage on invalidate it's perfectly fine for KVM to operate on idle >> ZONE_DEVICE pages. The common case is that ZONE_DEVICE pages are >> accessed and mapped while idle. Only direct-I/O temporarily marks them >> busy to synchronize with invalidate. KVM obviates that need by >> coordinating with mmu-notifiers instead. > Only the KVM MMU, e.g. page fault handler, coordinates via mmu_notifier, > the kvm_vcpu_map() case would continue using pages across an invalidate. Yes, and it gets/puts the page correctly. Paolo