[PATCH v2] block/nvme: Fix VFIO_MAP_DMA failed: No space left on device

[Philippe Mathieu-Daudé]

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-system-x86_64: block/block-backend.c:1968: blk_get_aio_context: 
Assertion `ctx == blk->ctx' failed.

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
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>
---
v2: KISS checking both errors undistinguishedly (Maxim)
---
 block/nvme.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/nvme.c b/block/nvme.c
index 2b5421e7aa6..c3d2a49866c 100644
--- a/block/nvme.c
+++ b/block/nvme.c
@@ -1030,7 +1030,7 @@ try_map:
         r = qemu_vfio_dma_map(s->vfio,
                               qiov->iov[i].iov_base,
                               len, true, &iova);
-        if (r == -ENOMEM && retry) {
+        if ((r == -ENOMEM || r == -ENOSPC) && retry) {
             retry = false;
             trace_nvme_dma_flush_queue_wait(s);
             if (s->dma_map_count) {
-- 
2.31.1