>-----Original Message-----
>From: Nicolin Chen <nicol...@nvidia.com>
>Subject: Re: [PATCH v5 20/21] Workaround for ERRATA_772415_SPR17
>
>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..
I'm not sure if VendorCaps struct wrapper is overprogramming as this ERRARA is
only VTD specific. We still need to check VendorCaps.vtd.flags bit.
>
>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;
> }
IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17 is a VTD specific flag bit from host
IOMMU, we have defined get_viommu_cap() to return pure vIOMMU capability bits,
so no host IOMMU flag bit can be returned here. See patch2 commit log for the
reason.
Thanks
Zhenzhong
