Re: [PATCH V1 2/3] amd-iommu: Sync IOVA-to-GPA translation during page invalidation

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 28 Sep 2020 15:05:05 -0500
Wei Huang <wei.huang2@amd.com> wrote:

> Add support to sync the IOVA-to-GPA translation at the time of IOMMU
> page invalidation. This function is called when two IOMMU commands,
> AMDVI_CMD_INVAL_AMDVI_PAGES and AMDVI_CMD_INVAL_AMDVI_ALL, are
> intercepted. Address space notifiers are called accordingly.
> 
> Co-developed-by: Wei Huang <wei.huang2@amd.com>
> Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
> ---
>  hw/i386/amd_iommu.c | 177 ++++++++++++++++++++++++++++++++++++++++++++
>  hw/i386/amd_iommu.h |  10 +++
>  hw/vfio/common.c    |   3 +-
>  3 files changed, 189 insertions(+), 1 deletion(-)
...
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 13471ae29436..243216499ce0 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -346,7 +346,8 @@ static int vfio_dma_map(VFIOContainer *container, hwaddr iova,
>       * the VGA ROM space.
>       */
>      if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0 ||
> -        (errno == EBUSY && vfio_dma_unmap(container, iova, size) == 0 &&
> +        ((errno == EEXIST || errno == EBUSY) &&
> +         vfio_dma_unmap(container, iova, size) == 0 &&
>           ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0)) {
>          return 0;
>      }


This seems like it should be a separate patch.  AFAICT the commit log
doesn't even hint at why this change is necessary.  I think the -EBUSY
error pre-dates vIOMMU as well.  Responding the same for an -EEXIST
almost suggests a coherency issue between QEMU and the kernel, or a
direct mapping replacement without an invalidation, which doesn't seem
to be what this patch is implementing.  Thanks,

Alex