[PATCH] virtio_mmio: Set DMA masks appropriately

Robin Murphy
2017-01-10T12:26:01Z

Once DMA API usage is enabled, it becomes apparent that virtio-mmio is
inadvertently relying on the default 32-bit DMA mask, which leads to
problems like rapidly exhausting SWIOTLB bounce buffers.

Ensure that we set the appropriate 64-bit DMA mask whenever possible,
with the coherent mask suitably limited for the legacy vring as per
a0be1db4304f ("virtio_pci: Limit DMA mask to 44 bits for legacy virtio
devices").

Reported-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Fixes: b42111382f0e ("virtio_mmio: Use the DMA API if enabled")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
drivers/virtio/virtio_mmio.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 48bfea91dbca..b5c5d49ca598 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -59,6 +59,7 @@
#define pr_fmt(fmt) "virtio-mmio: " fmt

#include <linux/acpi.h>
+#include <linux/dma-mapping.h>
#include <linux/highmem.h>
#include <linux/interrupt.h>
#include <linux/io.h>
@@ -497,6 +498,7 @@ static int virtio_mmio_probe(struct platform_device *pdev)
struct virtio_mmio_device *vm_dev;
struct resource *mem;
unsigned long magic;
+ int rc;

mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (!mem)
@@ -548,6 +550,14 @@ static int virtio_mmio_probe(struct platform_device *pdev)
if (vm_dev->version == 1)
writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_GUEST_PAGE_SIZE);

+ rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
+ if (rc)
+ rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
+ else if (vm_dev->version == 1)
+ dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32 + PAGE_SHIFT));
+ if (rc)
+ dev_warn(&pdev->dev, "Failed to enable 64-bit or 32-bit DMA. Trying to continue, but this might not work.\n");
+
platform_set_drvdata(pdev, vm_dev);

return register_virtio_device(&vm_dev->vdev);
--
2.10.2.dirty