Re: [RFC PATCH v5 2/4] util/vfio-helpers: Report error when IOMMU page size is not supported

[Fam Zheng <fam@euphon.net>]

On 2020-09-08 20:03, Philippe Mathieu-Daudé wrote:
> This driver uses the host page size to align its memory regions,
> but this size is not always compatible with the IOMMU. Add a
> check if the size matches, and bails out with listing the sizes
> the IOMMU supports.
> 
> Example on Aarch64:
> 
>  $ qemu-system-aarch64 -M virt -drive if=none,id=nvme0,file=nvme://0006:90:00.0/1,format=raw
>  qemu-system-aarch64: -drive if=none,id=nvme0,file=nvme://0006:90:00.0/1,format=raw: Unsupported IOMMU page size: 4 KiB
>  Available page size:
>   64 KiB
>   512 MiB
> 
> Suggested-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  util/vfio-helpers.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
> index 55b4107ce69..6d9ec7d365c 100644
> --- a/util/vfio-helpers.c
> +++ b/util/vfio-helpers.c
> @@ -11,6 +11,7 @@
>   */
>  
>  #include "qemu/osdep.h"
> +#include "qemu/cutils.h"
>  #include <sys/ioctl.h>
>  #include <linux/vfio.h>
>  #include "qapi/error.h"
> @@ -316,6 +317,25 @@ static int qemu_vfio_init_pci(QEMUVFIOState *s, const char *device,
>          ret = -errno;
>          goto fail;
>      }
> +    if (!(iommu_info.flags & VFIO_IOMMU_INFO_PGSIZES)) {
> +        error_setg(errp, "Failed to get IOMMU page size info");
> +        ret = -errno;

We don't have errno here, do we?

> +        goto fail;
> +    }
> +    if (!extract64(iommu_info.iova_pgsizes,
> +                   ctz64(qemu_real_host_page_size), 1)) {
> +        g_autofree char *host_page_size = size_to_str(qemu_real_host_page_size);
> +        error_setg(errp, "Unsupported IOMMU page size: %s", host_page_size);
> +        error_append_hint(errp, "Available page size:\n");
> +        for (int i = 0; i < 64; i++) {
> +            if (extract64(iommu_info.iova_pgsizes, i, 1)) {
> +                g_autofree char *iova_pgsizes = size_to_str(1UL << i);
> +                error_append_hint(errp, " %s\n", iova_pgsizes);

Interesting... Since it's printing page size which is fairly low level,
why not just plain (hex) numbers?

Fam

> +            }
> +        }
> +        ret = -EINVAL;
> +        goto fail;
> +    }
>  
>      s->device = ioctl(s->group, VFIO_GROUP_GET_DEVICE_FD, device);
>  
> -- 
> 2.26.2
> 
>