Re: [RFC PATCH v3 2/5] util/vfio-helpers: Report error on unsupported host architectures

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

On Tue, 18 Aug 2020 18:45:06 +0200
Philippe Mathieu-Daudé <philmd@redhat.com> wrote:

> The vfio-helpers implementation expects a TYPEv1 IOMMU, see
> qemu_vfio_init_pci:
> 
>   263     if (!ioctl(s->container, VFIO_CHECK_EXTENSION, VFIO_TYPE1_IOMMU)) {
>   264         error_setg_errno(errp, errno, "VFIO IOMMU check failed");
> 
> Thus POWER SPAPR IOMMU is obviously not supported.
> 
> The implementation only cares about host page size alignment
> (usually 4KB on X86), not the IOMMU one, which is be problematic
> on Aarch64, when 64MB page size is used. So Aarch64 is not
> supported neither.
> 
> Report an error when the host architecture is different than X86:
> 
>  $ qemu-system-aarch64 \
>     -drive file=nvme://0001:01:00.0/1,if=none,id=drive0 \
>     -device virtio-blk-pci,drive=drive0
>   qemu-system-aarch64: -drive file=nvme://0001:01:00.0/1,if=none,id=drive0: QEMU VFIO utility is not supported on this architecture
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Drew Jones <drjones@redhat.com>
> Cc: Laurent Vivier <lvivier@redhat.com>
> Cc: David Gibson <david@gibson.dropbear.id.au>
> ---
>  util/vfio-helpers.c | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
> index e399e330e26..60017936e3e 100644
> --- a/util/vfio-helpers.c
> +++ b/util/vfio-helpers.c
> @@ -420,14 +420,38 @@ static void qemu_vfio_open_common(QEMUVFIOState *s)
>      qemu_ram_foreach_block(qemu_vfio_init_ramblock, s);
>  }
>  
> +/**
> + * Return if the host architecture is supported.
> + *
> + * aarch64: IOMMU page alignment not respected
> + * ppc64:   SPAPR IOMMU window not configured
> + * x86-64:  Only architecture validated
> + * other:   Untested
> + */
> +static bool qemu_vfio_arch_supported(void)
> +{
> +    bool supported = false;
> +
> +#if defined(HOST_X86_64)
> +    supported = true;
> +#endif
> +
> +    return supported;
> +}

Why does this need to be hard coded to specific architectures rather
than probing for type1 IOMMU support and looking at the iova_pgsizes
from VFIO_IOMMU_GET_INFO to see if there's a compatible size?  It
requires us to get a bit deeper into the device initialization, but we
should still be able to unwind out of the device realize.  Otherwise
we're throwing out aarch64 running of 4KB for no reason, right?  Thanks,

Alex


>  /**
>   * Open a PCI device, e.g. "0000:00:01.0".
>   */
>  QEMUVFIOState *qemu_vfio_open_pci(const char *device, Error **errp)
>  {
>      int r;
> -    QEMUVFIOState *s = g_new0(QEMUVFIOState, 1);
> +    QEMUVFIOState *s;
>  
> +    if (!qemu_vfio_arch_supported()) {
> +        error_setg(errp,
> +                   "QEMU VFIO utility is not supported on this architecture");
> +        return NULL;
> +    }
> +    s = g_new0(QEMUVFIOState, 1);
>      r = qemu_vfio_init_pci(s, device, errp);
>      if (r) {
>          g_free(s);