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Tue, 12 Nov 2024 21:10:53 -0800 (PST) Message-ID: <89ae0aad-eb82-4f51-9384-689a19e1626d@gmail.com> Date: Wed, 13 Nov 2024 10:40:49 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v3 3/3] vhost: Allocate memory for packed vring From: Sahil Siddiq To: Eugenio Perez Martin References: <20240802112138.46831-1-sahilcdq@proton.me> <3311761.aeNJFYEL58@valdaarhun> <1904291.tdWV9SEqCh@valdaarhun> Content-Language: en-US Autocrypt: addr=icegambit91@gmail.com; keydata= xsDNBGcgaYEBDADpKUSKbchLCMdCuZGkuF50/7BiraKc8Ch+mk4T+2+E2/6qXAkalvCkFoqx 3/sa35rconZAFzB/r19e7i3UajIQjATvENrGxqe/IFqcJxo2Jr1HQBwCrsmlQoUCilSC6nDi ejcEIAFytJORDkCcZwLXPjdf5/4pbqVAW5823LB5j5F0TqHAnGY1RhS2V1eBPdRqjAA3xecT zTmLHlkqAXgM2DOot1KbycedZSieCwEykTXMaLC0/3Gyo2Cp1WTWOIyD0hsXpLyFioV4FaX2 Lm+z45Zc4PoNXeC6+l4PdDxixs+saAbadknP+9omwlb+PkMd3esq2wkowTwTJVJK8FCCNTo5 2OArA/ddxcyXY25JHN7vzGooFNW6Bb9YV+lbX6y95ytE3KcAmid73tQrcjlebIpgNAvOMyyZ BgQJY0HSu3DGNZuKtbNM3iTl82TFj7MVgkEffgF83N6XyBqDztIz2lN47/q5wyRi3jda9NDt geI+Nv145HjulO7bI3NT048AEQEAAc0kU2FoaWwgU2lkZGlxIDxpY2VnYW1iaXQ5MUBnbWFp bC5jb20+wsENBBMBCAA3FiEERtYfQYWFu+uAZjYrrzGlXdb6f1cFAmcgaYEFCQWjmoACGwME CwkIBwUVCAkKCwUWAgMBAAAKCRCvMaVd1vp/V/nnC/9KnNIr4a3JW3E/snxv1+XIyUmHBDLn PKBmLDYxO9RJe1xKo/sNmLEno4c8G1F/y12TLV086cpBYGKkE8mPMBABqxuiPG8srwoKc2HW bvoC2Zfeu/WeQ0YqeI9ZEwRhsDGQZ7vc8PnKnEUaPZn6iWW4GeX7dXWeGNrK0wU2B04l2d+M FIKaoPHk8w5Ff++QNcn0YRkm//nYlukHUrMxhNcuc18jaLLftOh7BH/4EbKtTN75KAFePQBi I2CbuC41fchTt12QrPB3yz1GKfudsEMLFHBNeComJNnuolPOq0YSyuKdRO8Jubn5ZqWQeTwj XbG7wTonDc8xe46irOhz36VcjsjSY+PYhVZSeDWeDUZgpaJkBjQDDodIN2eoMwVEyUByos9H mKrqrpBMmylOspAZzqjb5FtOqM0BCxQINdKKiMwRelSb6pHYCrbS0XzpwDUEpp7RWCbHgg+6 Ot72kQCEFxj2LzX9VxF24GGQy9inlUfN51IV04klSibtBuuz/NbOwM0EZyBpgQEMAJelVX4k CtCxD4Ji3FQ8LZs22z7VoUvqIb7Gj2lNvhPeijlqqBkSMIgnSCLxlH4ahqKnEV58IrfVriV0 92zb94Az2nl0r+bZYfvev1qCcVIYxk+pYYcRl5qPXX8XGalrkcBBWmkgTSwzNK9rV4850iVI hsJNel49qen9JwiFYMSKa2MYgdYSbeuuwXwUp0ZHeVFc5RnPK2wxws1xcnsdb9hRXs2UeTEE 0klG3HuXqJ96DzKrCieKHLjs330h+16gDWAFZSEoT7Mh3HFGI2dscVuBstQNgnwUMnsJv8jx c005CfLCjCBnJEhMd2/QFuLwCZv4IdoghKwYw18e61UbX2bFovo9dduD527pD4sFqi7U7ofv aO3yf+ulL6jiKypGvnbiBP3KY3aKxx6pHHH3aDc9eOqCUgrtS3+xt1du4+qxrYqEnrywFoJy 5zqSzbnTTjFpdTbY5SS52fIOktLlAKzEg6V9hkg2r08hC3/L4NVj6I4tsGZlqb2neRlHFmCr bQARAQABwsD8BBgBCAAmFiEERtYfQYWFu+uAZjYrrzGlXdb6f1cFAmcgaYIFCQWjmoACGwwA CgkQrzGlXdb6f1fDIgwAmpB7eL3XNSx3F+gbmksOPMqCU5rEswRedjEt6tBzFTXhdNFfhZTb vCddUNePZnzddgxAnDBcTqI1jx6Go6Hkti/mxJqXSczMYBsImD/lEm47axsADvpnNaEM+tmu m/cMKfpILUpy2Ey7CKXUA1vpzYeUD29EQWi0fxM0arplrVt/uzUdFRFQRn2hCqeDLBLONX1F Adq+re6M0dhKl4a2+erzZRIXh3vIGiDmpJEGrajrhqEnMXFp6toSiMGian94m8H3NT6rB64E JmdHgyjXADFbn2G5Mb6Pwa8KnnK1kYcZ+Pwu9LfMXfgI01Sh/k01hjUVmnpYep4nHUfwXA8r kn6WekD80DYbAfKyFAXQCO/nclZ82RNmJbDRi3AeMFrxKi6KgdGCp1Izhj9USaMOVqcuV2p0 Rsoq+sFqWOKaHWnQHCM9RkynQVqrgUaSawEbGlCP1KIhVmjfjVsmsCaKkUb9T6VeO+ZNe+Pn rPgMe6IIvn24UuW2f6fIt0AaqOWq Cc: sgarzare@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, Sahil Siddiq In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::62d; envelope-from=icegambit91@gmail.com; helo=mail-pl1-x62d.google.com X-Spam_score_int: -17 X-Spam_score: -1.8 X-Spam_bar: - X-Spam_report: (-1.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi, On 10/28/24 11:07 AM, Sahil Siddiq wrote: > [...] > The payload that VHOST_SET_VRING_BASE accepts depends on whether > split virtqueues or packed virtqueues are used [6]. In hw/virtio/vhost- > vdpa.c:vhost_vdpa_svq_setup() [7], the following payload is used which is > not suitable for packed virtqueues: > > struct vhost_vring_state s = { > .index = vq_index, > }; > > Based on the implementation in the linux kernel, the payload needs to > be as shown below for the ioctl to succeed for packed virtqueues: > > struct vhost_vring_state s = { > .index = vq_index, > .num = 0x80008000, > }; > > After making these changes, it looks like QEMU is able to set up the > virtqueues and shadow virtqueues are enabled as well. > > Unfortunately, before the L2 VM can finish booting the kernel crashes. > The reason is that even though packed virtqueues are to be used, the > kernel tries to run > drivers/virtio/virtio_ring.c:virtqueue_get_buf_ctx_split() [8] > (instead of virtqueue_get_buf_ctx_packed) and throws an "invalid vring > head" error. I am still investigating this issue. I made a mistake here. "virtqueue_get_buf_ctx_packed" [1] in the linux kernel also throws the same error. I think the issue might be because hw/virtio/vhost-vdpa.c:vhost_vdpa_svq_map_rings [2] does not handle mapping packed virtqueues at the moment. Probably because of this, vq->packed.desc_state[id].data [1] is NULL in the kernel. Regarding one of the earlier reviews in the same thread [3]: On 8/7/24 9:52 PM, Eugenio Perez Martin wrote: > On Fri, Aug 2, 2024 at 1:22 PM Sahil Siddiq wrote: >> >> Allocate memory for the packed vq format and support >> packed vq in the SVQ "start" and "stop" operations. >> >> Signed-off-by: Sahil Siddiq >> --- >> [...] >> >> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c >> index 4c308ee53d..f4285db2b4 100644 >> --- a/hw/virtio/vhost-shadow-virtqueue.c >> +++ b/hw/virtio/vhost-shadow-virtqueue.c >> [...] >> @@ -672,6 +674,16 @@ size_t vhost_svq_device_area_size(const VhostShadowVirtqueue *svq) >> return ROUND_UP(used_size, qemu_real_host_page_size()); >> } >> >> +size_t vhost_svq_memory_packed(const VhostShadowVirtqueue *svq) >> +{ >> + size_t desc_size = sizeof(struct vring_packed_desc) * svq->num_free; >> + size_t driver_event_suppression = sizeof(struct vring_packed_desc_event); >> + size_t device_event_suppression = sizeof(struct vring_packed_desc_event); >> + >> + return ROUND_UP(desc_size + driver_event_suppression + device_event_suppression, >> + qemu_real_host_page_size()); >> +} >> + >> /** >> * Set a new file descriptor for the guest to kick the SVQ and notify for avail >> * >> @@ -726,17 +738,30 @@ void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev, >> >> svq->vring.num = virtio_queue_get_num(vdev, virtio_get_queue_index(vq)); >> svq->num_free = svq->vring.num; >> - svq->vring.desc = mmap(NULL, vhost_svq_driver_area_size(svq), >> - PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, >> - -1, 0); >> - desc_size = sizeof(vring_desc_t) * svq->vring.num; >> - svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size); >> - svq->vring.used = mmap(NULL, vhost_svq_device_area_size(svq), >> - PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, >> - -1, 0); >> - svq->desc_state = g_new0(SVQDescState, svq->vring.num); >> - svq->desc_next = g_new0(uint16_t, svq->vring.num); >> - for (unsigned i = 0; i < svq->vring.num - 1; i++) { >> + svq->is_packed = virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED); >> + >> + if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED)) { >> + svq->vring_packed.vring.desc = mmap(NULL, vhost_svq_memory_packed(svq), >> + PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, >> + -1, 0); >> + desc_size = sizeof(struct vring_packed_desc) * svq->vring.num; >> + svq->vring_packed.vring.driver = (void *)((char *)svq->vring_packed.vring.desc + desc_size); >> + svq->vring_packed.vring.device = (void *)((char *)svq->vring_packed.vring.driver + >> + sizeof(struct vring_packed_desc_event)); > > This is a great start but it will be problematic when you start > mapping the areas to the vdpa device. The driver area should be read > only for the device, but it is placed in the same page as a RW one. > > More on this later. > >> + } else { >> + svq->vring.desc = mmap(NULL, vhost_svq_driver_area_size(svq), >> + PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, >> + -1, 0); >> + desc_size = sizeof(vring_desc_t) * svq->vring.num; >> + svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size); >> + svq->vring.used = mmap(NULL, vhost_svq_device_area_size(svq), >> + PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, >> + -1, 0); >> + } > > I think it will be beneficial to avoid "if (packed)" conditionals on > the exposed functions that give information about the memory maps. > These need to be replicated at > hw/virtio/vhost-vdpa.c:vhost_vdpa_svq_map_rings. Based on what I have understood, I'll need to have an if(packed) condition in vhost_vdpa_svq_map_rings() because the mappings will differ in the packed and split cases. > However, the current one depends on the driver area to live in the > same page as the descriptor area, so it is not suitable for this. Right, for the split case, svq->vring.desc and svq->vring.avail are mapped to the same page. svq->vring.desc = mmap(NULL, vhost_svq_driver_area_size(svq), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); desc_size = sizeof(vring_desc_t) * svq->vring.num; svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size); vhost_svq_driver_area_size() encompasses the descriptor area and avail ring. > So what about this action plan: > 1) Make the avail ring (or driver area) independent of the descriptor ring. > 2) Return the mapping permissions of the descriptor area (not needed > here, but needed for hw/virtio/vhost-vdpa.c:vhost_vdpa_svq_map_rings Does point 1 refer to mapping the descriptor and avail rings to separate pages for both split and packed cases. I am not sure if my understanding is correct. I believe, however, that this approach will make it easier to map the rings in the vdpa device. It might also help in removing the if(packed) condition in vhost_svq_start(). Thanks, Sahil [1] https://github.com/torvalds/linux/blob/master/drivers/virtio/virtio_ring.c#L1708 [2] https://gitlab.com/qemu-project/qemu/-/blob/master/hw/virtio/vhost-vdpa.c#L1178 [3] https://lists.nongnu.org/archive/html/qemu-devel/2024-08/msg01145.html