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([2001:b07:6468:f312:8dc6:5dd5:2c0a:6a9a]) by smtp.gmail.com with ESMTPSA id k19sm6238150wmi.42.2019.12.04.03.04.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Dec 2019 03:04:54 -0800 (PST) Subject: Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking To: Jason Wang , Peter Xu , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Sean Christopherson , "Dr . David Alan Gilbert" , Vitaly Kuznetsov , "Michael S. Tsirkin" References: <20191129213505.18472-1-peterx@redhat.com> <20191129213505.18472-5-peterx@redhat.com> <1355422f-ab62-9dc3-2b48-71a6e221786b@redhat.com> From: Paolo Bonzini Message-ID: Date: Wed, 4 Dec 2019 12:04:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <1355422f-ab62-9dc3-2b48-71a6e221786b@redhat.com> Content-Language: en-US X-MC-Unique: BNCD6OTNNSOUBu-pIXxETg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8 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 04/12/19 11:38, Jason Wang wrote: >> >> +=C2=A0=C2=A0=C2=A0 entry =3D &ring->dirty_gfns[ring->dirty_index & (rin= g->size - 1)]; >> +=C2=A0=C2=A0=C2=A0 entry->slot =3D slot; >> +=C2=A0=C2=A0=C2=A0 entry->offset =3D offset; >=20 >=20 > Haven't gone through the whole series, sorry if it was a silly question > but I wonder things like this will suffer from similar issue on > virtually tagged archs as mentioned in [1]. There is no new infrastructure to track the dirty pages---it's just a different way to pass them to userspace. > Is this better to allocate the ring from userspace and set to KVM > instead? Then we can use copy_to/from_user() friends (a little bit slow > on recent CPUs). Yeah, I don't think that would be better than mmap. Paolo > [1] https://lkml.org/lkml/2019/4/9/5