linux-kernel - [PATCH] virtio_ring: Fix querying of maximum DMA mapping size for virtio device

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Message-Id: <20211201112018.25276-1-will@kernel.org>
Date:   Wed,  1 Dec 2021 11:20:18 +0000
From:   Will Deacon <will@...nel.org>
To:     virtualization@...ts.linux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Subject: [PATCH] virtio_ring: Fix querying of maximum DMA mapping size for virtio device

virtio_max_dma_size() returns the maximum DMA mapping size of the virtio
device by querying dma_max_mapping_size() for the device when the DMA
API is in use for the vring. Unfortunately, the device passed is
initialised by register_virtio_device() and does not inherit the DMA
configuration from its parent, resulting in SWIOTLB errors when bouncing
is enabled and the default 256K mapping limit (IO_TLB_SEGSIZE) is not
respected:

  | virtio-pci 0000:00:01.0: swiotlb buffer is full (sz: 294912 bytes), total 1024 (slots), used 725 (slots)

Follow the pattern used elsewhere in the virtio_ring code when calling
into the DMA layer and pass the parent device to dma_max_mapping_size()
instead.

Cc: Marc Zyngier <maz@...nel.org>
Cc: Quentin Perret <qperret@...gle.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>
Signed-off-by: Will Deacon <will@...nel.org>
---
 drivers/virtio/virtio_ring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 6d2614e34470..028b05d44546 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -268,7 +268,7 @@ size_t virtio_max_dma_size(struct virtio_device *vdev)
 	size_t max_segment_size = SIZE_MAX;
 
 	if (vring_use_dma_api(vdev))
-		max_segment_size = dma_max_mapping_size(&vdev->dev);
+		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
 
 	return max_segment_size;
 }
-- 
2.34.0.rc2.393.gf8c9666880-goog