RE: [PATCH V2 1/4] intel-iommu: don't warn guest errors when getting rid2pasid entry

[Tian, Kevin]

> From: Jason Wang
> Sent: Monday, March 21, 2022 1:54 PM
> 
> We use to warn on wrong rid2pasid entry. But this error could be
> triggered by the guest and could happens during initialization. So
> let's don't warn in this case.
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  hw/i386/intel_iommu.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 874d01c162..90964b201c 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -1554,8 +1554,10 @@ static bool vtd_dev_pt_enabled(IntelIOMMUState
> *s, VTDContextEntry *ce)
>      if (s->root_scalable) {
>          ret = vtd_ce_get_rid2pasid_entry(s, ce, &pe);
>          if (ret) {
> -            error_report_once("%s: vtd_ce_get_rid2pasid_entry error: 
> %"PRId32,
> -                              __func__, ret);
> +            /*
> +             * This error is guest triggerable. We should assumt PT
> +             * not enabled for safety.
> +             */

suppose a VT-d fault should be queued in this case besides returning false:

SPD.1: A hardware attempt to access the scalable-mode PASID-directory 
entry referenced through the PASIDDIRPTR field in scalable-mode 
context-entry resulted in an error

SPT.1: A hardware attempt to access a scalable-mode PASID-table entry
referenced through the SMPTBLPTR field in a scalable-mode PASID-directory
entry resulted in an error.

Currently the implementation of vtd_ce_get_rid2pasid_entry() is also
problematic. According to VT-d spec, RID2PASID field is effective only
when ecap.rps is true otherwise PASID#0 is used for RID2PASID. I didn't
see ecap.rps is set, neither is it checked in that function. It works possibly
just because Linux currently programs 0 to RID2PASID...

>              return false;
>          }
>          return (VTD_PE_GET_TYPE(&pe) == VTD_SM_PASID_ENTRY_PT);
> --
> 2.25.1
>