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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Aug 03, 2026 at 05:40:06AM +0000, Clément MATHIEU--DRIF wrote:
> 
> 
> On Sun, 2026-08-02 at 14:53 -0400, Michael S. Tsirkin wrote:
> > Caution: External email. Do not open attachments or click links, unless this email comes from a known sender and you know the content is safe.
> > 
> > 
> > On Sun, Aug 02, 2026 at 04:05:08PM +0000, Clément MATHIEU--DRIF wrote:
> > 
> > > SVM in Linux requires SMPWC as of 780dfed68862.
> > 
> > 
> > And what is 780dfed68862?
> 
> A commit in the linux tree, is there a dedicated tag for that?
> 
> Maybe "Link: link_to_github"?

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=780dfed68862


> > 
> > 
> > > This is free in the
> > > current implementation as it is already in line with the expected
> > > behaviour.
> > > 
> > > Signed-off-by: Clement Mathieu--Drif <[clement.mathieu--drif@bull.com](mailto:clement.mathieu--drif@bull.com)>
> > > ---
> > >  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 */
> > > --
> > > 2.54.0
> > 
> >