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Tsirkin" To: Jason Wang Subject: Re: [RFC PATCH V2 0/7] Do not read from descripto ring Message-ID: <20210506041057-mutt-send-email-mst@kernel.org> References: <20210423080942.2997-1-jasowang@redhat.com> <0e9d70b7-6c8a-4ff5-1fa9-3c4f04885bb8@redhat.com> MIME-Version: 1.0 In-Reply-To: <0e9d70b7-6c8a-4ff5-1fa9-3c4f04885bb8@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: ashish.kalra@amd.com, file@sect.tu-berlin.de, kvm@vger.kernel.org, konrad.wilk@oracle.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, hch@infradead.org, xieyongji@bytedance.com, stefanha@redhat.com X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; 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(version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 May 2021 01:12:20 -0700 (PDT) Date: Thu, 6 May 2021 04:12:17 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, xieyongji@bytedance.com, stefanha@redhat.com, file@sect.tu-berlin.de, ashish.kalra@amd.com, konrad.wilk@oracle.com, kvm@vger.kernel.org, hch@infradead.org Subject: Re: [RFC PATCH V2 0/7] Do not read from descripto ring Message-ID: <20210506041057-mutt-send-email-mst@kernel.org> References: <20210423080942.2997-1-jasowang@redhat.com> <0e9d70b7-6c8a-4ff5-1fa9-3c4f04885bb8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <0e9d70b7-6c8a-4ff5-1fa9-3c4f04885bb8@redhat.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, May 06, 2021 at 11:20:30AM +0800, Jason Wang wrote: > > 在 2021/4/23 下午4:09, Jason Wang 写道: > > Hi: > > > > Sometimes, the driver doesn't trust the device. This is usually > > happens for the encrtpyed VM or VDUSE[1]. In both cases, technology > > like swiotlb is used to prevent the poking/mangling of memory from the > > device. But this is not sufficient since current virtio driver may > > trust what is stored in the descriptor table (coherent mapping) for > > performing the DMA operations like unmap and bounce so the device may > > choose to utilize the behaviour of swiotlb to perform attacks[2]. > > > > To protect from a malicous device, this series store and use the > > descriptor metadata in an auxiliay structure which can not be accessed > > via swiotlb instead of the ones in the descriptor table. This means > > the descriptor table is write-only from the view of the driver. > > > > Actually, we've almost achieved that through packed virtqueue and we > > just need to fix a corner case of handling mapping errors. For split > > virtqueue we just follow what's done in the packed. > > > > Note that we don't duplicate descriptor medata for indirect > > descriptors since it uses stream mapping which is read only so it's > > safe if the metadata of non-indirect descriptors are correct. > > > > For split virtqueue, the change increase the footprint due the the > > auxiliary metadata but it's almost neglectlable in the simple test > > like pktgen or netpef. > > > > Slightly tested with packed on/off, iommu on/of, swiotlb force/off in > > the guest. > > > > Please review. > > > > Changes from V1: > > - Always use auxiliary metadata for split virtqueue > > - Don't read from descripto when detaching indirect descriptor > > > Hi Michael: > > Our QE see no regression on the perf test for 10G but some regressions > (5%-10%) on 40G card. > > I think this is expected since we increase the footprint, are you OK with > this and we can try to optimize on top or you have other ideas? > > Thanks Let's try for just a bit, won't make this window anyway: I have an old idea. Add a way to find out that unmap is a nop (or more exactly does not use the address/length). Then in that case even with DMA API we do not need the extra data. Hmm? > > > > > [1] > > https://lore.kernel.org/netdev/fab615ce-5e13-a3b3-3715-a4203b4ab010@redhat.com/T/ > > [2] > > https://yhbt.net/lore/all/c3629a27-3590-1d9f-211b-c0b7be152b32@redhat.com/T/#mc6b6e2343cbeffca68ca7a97e0f473aaa871c95b > > > > Jason Wang (7): > > virtio-ring: maintain next in extra state for packed virtqueue > > virtio_ring: rename vring_desc_extra_packed > > virtio-ring: factor out desc_extra allocation > > virtio_ring: secure handling of mapping errors > > virtio_ring: introduce virtqueue_desc_add_split() > > virtio: use err label in __vring_new_virtqueue() > > virtio-ring: store DMA metadata in desc_extra for split virtqueue > > > > drivers/virtio/virtio_ring.c | 201 +++++++++++++++++++++++++---------- > > 1 file changed, 144 insertions(+), 57 deletions(-) > >