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

[Jason Wang]

On Thu, Mar 24, 2022 at 4:21 PM Tian, Kevin <kevin.tian@intel.com> wrote:
>
> > 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.

Probably, but this issue is not introduced in this patch. We can fix
it on top if necessary.

>
> 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...

This seems to be another issue since the introduction of scalable mode.

Thanks

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