Do not call dma_max_mapping_size for devices that have no DMA
mask set, otherwise we can hit a NULL pointer dereference.
This occurs when a virtio-blk-pci device is protected with
a virtual IOMMU.
Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
Signed-off-by: Eric Auger <[email protected]>
Suggested-by: Christoph Hellwig <[email protected]>
---
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 c8be1c4f5b55..37c143971211 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -262,7 +262,7 @@ size_t virtio_max_dma_size(struct virtio_device *vdev)
{
size_t max_segment_size = SIZE_MAX;
- if (vring_use_dma_api(vdev))
+ if (vring_use_dma_api(vdev) && vdev->dev.dma_mask)
max_segment_size = dma_max_mapping_size(&vdev->dev);
return max_segment_size;
--
2.20.1
On Wed, Jul 24, 2019 at 06:10:53PM -0400, Michael S. Tsirkin wrote:
> Christoph - would a documented API wrapping dma_mask make sense?
> With the documentation explaining how users must
> desist from using DMA APIs if that returns false ...
We have some bigger changes in this are planned, including turning
dma_mask into a scalar instead of a pointer, please stay tuned.
On Thu, Jul 25, 2019 at 01:53:49PM +0200, Auger Eric wrote:
> I am confused: if vring_use_dma_api() returns false if the dma_mask is
> unset (ie. vring_use_dma_api() returns false), the virtio-blk-pci device
> will not be able to get translated addresses and won't work properly.
>
> The patch above allows the dma api to be used and only influences the
> max_segment_size and it works properly.
>
> So is it normal the dma_mask is unset in my case?
Its not normal. I assume you use virtio-nmio? Due to the mess with
the dma_mask being a pointer a lot of subsystems forgot to set a dma
mask up, and oddly enough seem to mostly get away with it.
Hi Christoph, Michael,
On 7/25/19 3:04 PM, Christoph Hellwig wrote:
> On Thu, Jul 25, 2019 at 01:53:49PM +0200, Auger Eric wrote:
>> I am confused: if vring_use_dma_api() returns false if the dma_mask is
>> unset (ie. vring_use_dma_api() returns false), the virtio-blk-pci device
>> will not be able to get translated addresses and won't work properly.
>>
>> The patch above allows the dma api to be used and only influences the
>> max_segment_size and it works properly.
>>
>> So is it normal the dma_mask is unset in my case?
>
> Its not normal. I assume you use virtio-nmio? Due to the mess with
> the dma_mask being a pointer a lot of subsystems forgot to set a dma
> mask up, and oddly enough seem to mostly get away with it.
>
No the issue is encountered with virtio-blk-pci
I think the problem is virtio_max_dma_size() is called from
virtblk_probe (virtio_blk.c) on the virtio<n> device and not the actual
virtio_pci_device which has a dma_mask set. I don't think the virtio<n>
device ever has a dma_mask set.
We do not hit the guest crash on the virtio-net-pci device as the
virtio-net driver does not call virtio_max_dma_size() on the virtio<n>
device.
Does fd1068e1860e ("virtio-blk: Consider virtio_max_dma_size() for
maximum segment size") call virtio_max_dma_size() on the right device?
Thanks
Eric