[PATCH] 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 -ENOSPC error when DMA mappings are exhausted;
other errors (such -ENOMEM) are still handled later in the same
function.

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>
---
Michal, is it still possible for you to test this (old bug)?

A functional test using viommu & nested VM is planned (suggested by
Stefan and Maxim).
---
 block/nvme.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/nvme.c b/block/nvme.c
index 2b5421e7aa6..12f9dd5cce3 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 == -ENOSPC && retry) {
             retry = false;
             trace_nvme_dma_flush_queue_wait(s);
             if (s->dma_map_count) {
-- 
2.31.1