Re: [PATCH-for-6.1 v3] block/nvme: Fix VFIO_MAP_DMA failed: No space left on device

[Stefan Hajnoczi]

On Fri, Jul 23, 2021 at 09:58:43PM +0200, Philippe Mathieu-Daudé wrote:
> When the NVMe block driver was introduced (see commit bdd6a90a9e5,
> January 2018), Linux VFIO_IOMMU_MAP_DMA ioctl was only returning
> -ENOMEM in case of error. The driver was correctly handling the
> error path to recycle its volatile IOVA mappings.
> 
> To fix CVE-2019-3882, Linux commit 492855939bdb ("vfio/type1: Limit
> DMA mappings per container", April 2019) added the -ENOSPC error to
> signal the user exhausted the DMA mappings available for a container.
> 
> The block driver started to mis-behave:
> 
>   qemu-system-x86_64: VFIO_MAP_DMA failed: No space left on device
>   (qemu)
>   (qemu) info status
>   VM status: paused (io-error)
>   (qemu) c
>   VFIO_MAP_DMA failed: No space left on device
>   (qemu) c
>   VFIO_MAP_DMA failed: No space left on device
> 
> (The VM is not resumable from here, hence stuck.)
> 
> Fix by handling the new -ENOSPC error (when DMA mappings are
> exhausted) without any distinction to the current -ENOMEM error,
> so we don't change the behavior on old kernels where the CVE-2019-3882
> fix is not present.
> 
> An easy way to reproduce this bug is to restrict the DMA mapping
> limit (65535 by default) when loading the VFIO IOMMU module:
> 
>   # modprobe vfio_iommu_type1 dma_entry_limit=666
> 
> Cc: qemu-stable@nongnu.org
> Cc: Fam Zheng <fam@euphon.net>
> Cc: Maxim Levitsky <mlevitsk@redhat.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Reported-by: Michal Prívozník <mprivozn@redhat.com>
> Fixes: bdd6a90a9e5 ("block: Add VFIO based NVMe driver")
> Buglink: https://bugs.launchpad.net/qemu/+bug/1863333
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/65
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> v3: Reworded (Fam)
> v2: KISS checking both errors undistinguishedly (Maxim)
> ---
>  block/nvme.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)

Thanks, applied to my block tree:
https://gitlab.com/stefanha/qemu/commits/block

Stefan

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