Re: [RFC v2 10/22] intel_iommu: add virtual command capability support

[Peter Xu]

On Wed, Nov 06, 2019 at 12:40:41PM +0000, Liu, Yi L wrote:
> > 
> > Do you know what should happen on bare-metal from spec-wise that when
> > the guest e.g. writes 2 bytes to these mmio regions?
> 
> I've no idea to your question. It is not a bare-metal capability. Personally, 
> I
> prefer to have a toggle bit to mark the full written of a cmd to VMCD_REG.
> Reason is that we have no control on guest software. It may write new cmd
> to VCMD_REG in a bad manner. e.g. write high 32 bits first and then write the
> low 32 bits. Then it will have two traps. Apparently, for the first trap, it 
> fills
> in the VCMD_REG and no need to handle it since it is not a full written. I'm
> checking it and evaluating it. How do you think on it?

Oh I just noticed that vtd_mem_ops.min_access_size==4 now so writting
2B should never happen at least.  Then we'll bail out at
memory_region_access_valid().  Seems fine.

> 
> > 
> > > +        if (!vtd_handle_vcmd_write(s, val)) {
> > > +            vtd_set_long(s, addr, val);
> > > +        }
> > > +        break;
> > > +
> > >      default:
> > >          if (size == 4) {
> > >              vtd_set_long(s, addr, val);
> > > @@ -3617,7 +3769,8 @@ static void vtd_init(IntelIOMMUState *s)
> > >              s->ecap |= VTD_ECAP_SMTS | VTD_ECAP_SRS | VTD_ECAP_SLTS;
> > >          } else if (!strcmp(s->scalable_mode, "modern")) {
> > >              s->ecap |= VTD_ECAP_SMTS | VTD_ECAP_SRS | VTD_ECAP_PASID
> > > -                       | VTD_ECAP_FLTS | VTD_ECAP_PSS;
> > > +                       | VTD_ECAP_FLTS | VTD_ECAP_PSS | VTD_ECAP_VCS;
> > > +            s->vccap |= VTD_VCCAP_PAS;
> > >          }
> > >      }
> > >
> > 
> > [...]
> > 
> > > +#define VTD_VCMD_CMD_MASK           0xffUL
> > > +#define VTD_VCMD_PASID_VALUE(val)   (((val) >> 8) & 0xfffff)
> > > +
> > > +#define VTD_VCRSP_RSLT(val)         ((val) << 8)
> > > +#define VTD_VCRSP_SC(val)           (((val) & 0x3) << 1)
> > > +
> > > +#define VTD_VCMD_UNDEFINED_CMD         1ULL
> > > +#define VTD_VCMD_NO_AVAILABLE_PASID    2ULL
> > 
> > According to 10.4.44 - should this be 1?
> 
> It's 2 now per VT-d spec 3.1 (2019 June). I should have mentioned it in the 
> cover
> letter...

Well you're right... I hope there won't be other "major" things get
changed otherwise it'll be really a pain of working on all of these
before things settle...

Thanks,

-- 
Peter Xu