Re: [PATCH v10 09/10] virtio-iommu: Set supported page size mask

[Auger Eric <eric.auger@redhat.com>]

Hi Jean,

On 10/8/20 7:15 PM, Jean-Philippe Brucker wrote:
> From: Bharat Bhushan <bbhushan2@marvell.com>
> 
> The virtio-iommu device can deal with arbitrary page sizes for virtual
> endpoints, but for endpoints assigned with VFIO it must follow the page
> granule used by the host IOMMU driver.
> 
> Implement the interface to set the vIOMMU page size mask, called by VFIO
> for each endpoint. We assume that all host IOMMU drivers use the same
> page granule (the host page granule). Override the page_size_mask field
> in the virtio config space.
> 
> Signed-off-by: Bharat Bhushan <bbhushan2@marvell.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

> ---
> v10: Use global page mask, allowing VFIO to override it until boot.
> ---
>  hw/virtio/virtio-iommu.c | 51 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
> 
> diff --git a/hw/virtio/virtio-iommu.c b/hw/virtio/virtio-iommu.c
> index 8823bfc804a..dd0b3093d1b 100644
> --- a/hw/virtio/virtio-iommu.c
> +++ b/hw/virtio/virtio-iommu.c
> @@ -914,6 +914,56 @@ static int virtio_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu_mr,
>      return 0;
>  }
>  
> +static int virtio_iommu_set_page_size_mask(IOMMUMemoryRegion *mr,
> +                                           uint64_t page_size_mask,
> +                                           Error **errp)
> +{
> +    int new_granule, old_granule;
> +    IOMMUDevice *sdev = container_of(mr, IOMMUDevice, iommu_mr);
> +    VirtIOIOMMU *s = sdev->viommu;
> +
> +    if (!page_size_mask) {
set errp
> +        return -1;
> +    }
> +
> +    new_granule = ctz64(page_size_mask);
> +    old_granule = ctz64(s->config.page_size_mask);

I think this would be interesting to add a trace point
> +
> +    /*
> +     * Modifying the page size after machine initialization isn't supported.
> +     * Having a different mask is possible but the guest will use sub-optimal
> +     * block sizes, so warn about it.
> +     */
> +    if (qdev_hotplug) {
> +        if (new_granule != old_granule) {
> +            error_setg(errp,
> +                       "virtio-iommu page mask 0x%"PRIx64
> +                       " is incompatible with mask 0x%"PRIx64,
> +                       s->config.page_size_mask, page_size_mask);
> +            return -1;
> +        } else if (page_size_mask != s->config.page_size_mask) {
> +            warn_report("virtio-iommu page mask 0x%"PRIx64
> +                        " does not match 0x%"PRIx64,
> +                        s->config.page_size_mask, page_size_mask);
> +        }
> +        return 0;
> +    }
> +
> +    /*
> +     * Disallow shrinking the page size. For example if an endpoint only
> +     * supports 64kB pages, we can't globally enable 4kB pages. But that
> +     * shouldn't happen, the host is unlikely to setup differing page granules.
> +     * The other bits are only hints describing optimal block sizes.
> +     */
> +    if (new_granule < old_granule) {
> +        error_setg(errp, "memory region shrinks the virtio-iommu page granule");
> +        return -1;
> +    }
> +
> +    s->config.page_size_mask = page_size_mask;
> +    return 0;
> +}
> +
>  static void virtio_iommu_device_realize(DeviceState *dev, Error **errp)
>  {
>      VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> @@ -1146,6 +1196,7 @@ static void virtio_iommu_memory_region_class_init(ObjectClass *klass,
>      imrc->translate = virtio_iommu_translate;
>      imrc->replay = virtio_iommu_replay;
>      imrc->notify_flag_changed = virtio_iommu_notify_flag_changed;
> +    imrc->iommu_set_page_size_mask = virtio_iommu_set_page_size_mask;
>  }
>  
>  static const TypeInfo virtio_iommu_info = {
> 
Thanks

Eric