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[80.230.31.118]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432613f7e6esm57256214f8f.21.2025.12.30.02.16.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Dec 2025 02:16:21 -0800 (PST) Date: Tue, 30 Dec 2025 05:16:18 -0500 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Cong Wang , Jonathan Corbet , Olivia Mackall , Herbert Xu , Jason Wang , Paolo Bonzini , Stefan Hajnoczi , Eugenio =?utf-8?B?UMOpcmV6?= , "James E.J. Bottomley" , "Martin K. Petersen" , Gerd Hoffmann , Xuan Zhuo , Marek Szyprowski , Robin Murphy , Stefano Garzarella , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Petr Tesarik , Leon Romanovsky , Jason Gunthorpe , linux-doc@vger.kernel.org, linux-crypto@vger.kernel.org, virtualization@lists.linux.dev, linux-scsi@vger.kernel.org, iommu@lists.linux.dev, kvm@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH RFC 10/13] virtio_scsi: fix DMA cacheline issues for events Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Current struct virtio_scsi_event_node layout has two problems: The event (DMA_FROM_DEVICE) and work (CPU-written via INIT_WORK/queue_work) fields share a cacheline. On non-cache-coherent platforms, CPU writes to work can corrupt device-written event data. If DMA_MIN_ALIGN is large enough, the 8 events in event_list share cachelines, triggering CONFIG_DMA_API_DEBUG warnings. Fix the corruption by moving event buffers to a separate array and aligning using __dma_from_device_aligned_begin/end. Suppress the (now spurious) DMA debug warnings using virtqueue_add_inbuf_cache_clean(). Signed-off-by: Michael S. Tsirkin --- drivers/scsi/virtio_scsi.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c index 96a69edddbe5..b0ce3884e22a 100644 --- a/drivers/scsi/virtio_scsi.c +++ b/drivers/scsi/virtio_scsi.c @@ -29,6 +29,7 @@ #include #include #include +#include =20 #include "sd.h" =20 @@ -61,7 +62,7 @@ struct virtio_scsi_cmd { =20 struct virtio_scsi_event_node { struct virtio_scsi *vscsi; - struct virtio_scsi_event event; + struct virtio_scsi_event *event; struct work_struct work; }; =20 @@ -89,6 +90,12 @@ struct virtio_scsi { =20 struct virtio_scsi_vq ctrl_vq; struct virtio_scsi_vq event_vq; + + /* DMA buffers for events - aligned, kept separate from CPU-written field= s */ + __dma_from_device_aligned_begin + struct virtio_scsi_event events[VIRTIO_SCSI_EVENT_LEN]; + __dma_from_device_aligned_end + struct virtio_scsi_vq req_vqs[]; }; =20 @@ -237,12 +244,12 @@ static int virtscsi_kick_event(struct virtio_scsi *vs= csi, unsigned long flags; =20 INIT_WORK(&event_node->work, virtscsi_handle_event); - sg_init_one(&sg, &event_node->event, sizeof(struct virtio_scsi_event)); + sg_init_one(&sg, event_node->event, sizeof(struct virtio_scsi_event)); =20 spin_lock_irqsave(&vscsi->event_vq.vq_lock, flags); =20 - err =3D virtqueue_add_inbuf(vscsi->event_vq.vq, &sg, 1, event_node, - GFP_ATOMIC); + err =3D virtqueue_add_inbuf_cache_clean(vscsi->event_vq.vq, &sg, 1, event= _node, + GFP_ATOMIC); if (!err) virtqueue_kick(vscsi->event_vq.vq); =20 @@ -257,6 +264,7 @@ static int virtscsi_kick_event_all(struct virtio_scsi *= vscsi) =20 for (i =3D 0; i < VIRTIO_SCSI_EVENT_LEN; i++) { vscsi->event_list[i].vscsi =3D vscsi; + vscsi->event_list[i].event =3D &vscsi->events[i]; virtscsi_kick_event(vscsi, &vscsi->event_list[i]); } =20 @@ -380,7 +388,7 @@ static void virtscsi_handle_event(struct work_struct *w= ork) struct virtio_scsi_event_node *event_node =3D container_of(work, struct virtio_scsi_event_node, work); struct virtio_scsi *vscsi =3D event_node->vscsi; - struct virtio_scsi_event *event =3D &event_node->event; + struct virtio_scsi_event *event =3D event_node->event; =20 if (event->event & cpu_to_virtio32(vscsi->vdev, VIRTIO_SCSI_T_EVENTS_MISSED)) { --=20 MST