Re: [PATCH v1] intel_iommu: Expose SMPWC when SVM is enabled

On Tue, 2026-08-04 at 16:51 +0800, Yi Liu wrote:
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> 
> 
> On 8/3/26 00:47, Michael S. Tsirkin wrote:
> 
> > On Sun, Aug 02, 2026 at 04:05:08PM +0000, Clément MATHIEU--DRIF wrote:
> > 
> > > SVM in Linux requires SMPWC as of 780dfed68862. This is free in the
> > > current implementation as it is already in line with the expected
> > > behaviour.
> > > 
> > > Signed-off-by: Clement Mathieu--Drif <[[email protected]](mailto:[email protected])>
> > > ---
> > >   hw/i386/intel_iommu.c          | 3 ++-
> > >   hw/i386/intel_iommu_internal.h | 1 +
> > >   2 files changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> > > index 8245452d89..9f21622a4f 100644
> > > --- a/hw/i386/intel_iommu.c
> > > +++ b/hw/i386/intel_iommu.c
> > > @@ -5108,7 +5108,8 @@ static void vtd_init(IntelIOMMUState *s)
> > >       }
> > > 
> > >       if (s->svm) {
> > > -        s->ecap |= VTD_ECAP_PRS | VTD_ECAP_PDS | VTD_ECAP_NWFS;
> > > +        s->ecap |= VTD_ECAP_PRS | VTD_ECAP_PDS | VTD_ECAP_NWFS |
> > > +                   VTD_ECAP_SMPWCS;
> > >       }
> > > 
> > >       vtd_reset_caches(s);
> > > diff --git a/hw/i386/intel_iommu_internal.h b/hw/i386/intel_iommu_internal.h
> > > index 924e91cb8a..df7a0efa6e 100644
> > > --- a/hw/i386/intel_iommu_internal.h
> > > +++ b/hw/i386/intel_iommu_internal.h
> > > @@ -202,6 +202,7 @@
> > >   #define VTD_ECAP_SMTS               (1ULL << 43)
> > >   #define VTD_ECAP_SSTS               (1ULL << 46)
> > >   #define VTD_ECAP_FSTS               (1ULL << 47)
> > > +#define VTD_ECAP_SMPWCS             (1ULL << 48)
> > > 
> > >   /* CAP_REG */
> > >   /* (offset >> 4) << 24 */
> > 
> > 
> > Any cross version migration concerns with this one?
> 
> 
> this bit is exposed when the svm flag is set. This flag was introduced  
> by the below commit and controlled by a 'svm' option. So looks like this  
> change is ok from the migration perspective?

I came to the same conclusion.

Thanks

> 
> 
> 952e1a6e90eb22a6deffa4e980277b135e9d077f
> 
> @@ -4186,6 +4188,7 @@ static const Property vtd_properties[] = {  
>       DEFINE_PROP_BOOL("x-flts", IntelIOMMUState, fsts, FALSE),  
>       DEFINE_PROP_BOOL("snoop-control", IntelIOMMUState, snoop_control,  
> false),  
>       DEFINE_PROP_BOOL("x-pasid-mode", IntelIOMMUState, pasid, false),  
> +    DEFINE_PROP_BOOL("svm", IntelIOMMUState, svm, false),  
>       DEFINE_PROP_BOOL("dma-drain", IntelIOMMUState, dma_drain, true),  
>       DEFINE_PROP_BOOL("stale-tm", IntelIOMMUState, stale_tm, false),  
>       DEFINE_PROP_BOOL("fs1gp", IntelIOMMUState, fs1gp, true),
>