linux-kernel - [PATCH 4.9 61/66] virtio_mmio: Set DMA masks appropriately

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Date:   Tue, 31 Jan 2017 06:37:05 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Robin Murphy <robin.murphy@....com>
Subject: [PATCH 4.9 61/66] virtio_mmio: Set DMA masks appropriately

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Robin Murphy <robin.murphy@....com>

commit f7f6634d23830ff74335734fbdb28ea109c1f349 upstream.

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").

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Michael S. Tsirkin <mst@...hat.com>
Reported-by: Jean-Philippe Brucker <jean-philippe.brucker@....com>
Fixes: b42111382f0e ("virtio_mmio: Use the DMA API if enabled")
Signed-off-by: Robin Murphy <robin.murphy@....com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/virtio/virtio_mmio.c |   20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

--- 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 plat
 	struct virtio_mmio_device *vm_dev;
 	struct resource *mem;
 	unsigned long magic;
+	int rc;
 
 	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	if (!mem)
@@ -545,9 +547,25 @@ static int virtio_mmio_probe(struct plat
 	}
 	vm_dev->vdev.id.vendor = readl(vm_dev->base + VIRTIO_MMIO_VENDOR_ID);
 
-	if (vm_dev->version == 1)
+	if (vm_dev->version == 1) {
 		writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_GUEST_PAGE_SIZE);
 
+		rc = dma_set_mask(&pdev->dev, DMA_BIT_MASK(64));
+		/*
+		 * In the legacy case, ensure our coherently-allocated virtio
+		 * ring will be at an address expressable as a 32-bit PFN.
+		 */
+		if (!rc)
+			dma_set_coherent_mask(&pdev->dev,
+					      DMA_BIT_MASK(32 + PAGE_SHIFT));
+	} else {
+		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));
+	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);