Re: [PATCH v5 20/21] Workaround for ERRATA_772415_SPR17

[Nicolin Chen]

On Fri, Aug 22, 2025 at 02:40:58AM -0400, Zhenzhong Duan wrote:
> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
> index e503c232e1..59735e878c 100644
> --- a/hw/vfio/iommufd.c
> +++ b/hw/vfio/iommufd.c
> @@ -324,6 +324,7 @@ static bool iommufd_cdev_autodomains_get(VFIODevice 
> *vbasedev,
>  {
>      ERRP_GUARD();
>      IOMMUFDBackend *iommufd = vbasedev->iommufd;
> +    struct iommu_hw_info_vtd vtd;

VendorCaps vendor_caps;

>      uint32_t type, flags = 0;
>      uint64_t hw_caps;
>      VFIOIOASHwpt *hwpt;
> @@ -371,10 +372,15 @@ static bool iommufd_cdev_autodomains_get(VFIODevice 
> *vbasedev,
>       * instead.
>       */
>      if (!iommufd_backend_get_device_info(vbasedev->iommufd, vbasedev->devid,
> -                                         &type, NULL, 0, &hw_caps, errp)) {
> +                                         &type, &vtd, sizeof(vtd), &hw_caps,

s/vtd/vendor_caps/g

> +                                         errp)) {
>          return false;
>      }
>  
> +    if (vtd.flags & IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17) {
> +        container->bcontainer.bypass_ro = true;

This circled back to checking a vendor specific flag in the core..

Perhaps we could upgrade the get_viommu_cap op and its API:

enum viommu_flags {
    VIOMMU_FLAG_HW_NESTED = BIT_ULL(0),
    VIOMMU_FLAG_BYPASS_RO = BIT_ULL(1),
};

bool vfio_device_get_viommu_flags(VFIODevice *vbasedev, VendorCaps *vendor_caps,
                                  uint64_t *viommu_flags);

Then:
    if (viommu_flags & VIOMMU_FLAG_BYPASS_RO) {
        container->bcontainer.bypass_ro = true;
    }
...
    if (viommu_flags & VIOMMU_FLAG_HW_NESTED) {
        flags |= IOMMU_HWPT_ALLOC_NEST_PARENT;
    }

Nicolin