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    SubjectRe: [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call
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    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

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