Re: [Xen-devel] [PATCH v6 04/18] vt-d: VT-d Posted-Interrupts feature detection

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Friday, September 04, 2015 10:31 PM
> To: Wu, Feng
> Cc: Tian, Kevin; Zhang, Yang Z; xen-devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH v6 04/18] vt-d: VT-d Posted-Interrupts feature
> detection
> 
> >>> On 25.08.15 at 03:57, <feng.wu@xxxxxxxxx> wrote:
> > --- a/xen/drivers/passthrough/vtd/iommu.c
> > +++ b/xen/drivers/passthrough/vtd/iommu.c
> > @@ -2079,6 +2079,9 @@ static int init_vtd_hw(void)
> >                  disable_intremap(drhd->iommu);
> >      }
> >
> > +    if ( !iommu_intremap )
> > +        iommu_intpost = 0;
> 
> Why is this being repeated here? iommu_setup() is already taking
> care of this thanks to the earlier patch.

Here is my original thought, we have two path to get here as below:

iommu_setup() -> ... -> int_vtd_hw()
vtd_resume() -> ... -> int_vtd_hw()

I added the logic here to cover the 'vtd_resume()' case, however,
after thinking more, seems I don't need to do this, because the
logic has been done before resume, it should be there after back,
right?

> 
> > @@ -2176,6 +2179,14 @@ int __init intel_vtd_setup(void)
> >          if ( iommu_intremap && !ecap_intr_remap(iommu->ecap) )
> >              iommu_intremap = 0;
> >
> > +        /*
> > +         * We cannot use posted interrupt if X86_FEATURE_CX16 is
> > +         * not supported, since we count on this feature to
> > +         * atomically update 16-byte IRTE in posted format.
> > +         */
> > +        if ( !iommu_intremap || !cap_intr_post(iommu->cap)
> || !cpu_has_cx16 )
> > +            iommu_intpost = 0;
> 
> You should check iommu_intpost instead of iommu_intremap to
> match the other checks above here.

Here I followed your advice:
http://lists.xenproject.org/archives/html/xen-devel/2015-06/msg01261.html

I think the following code should be ok here though, if you like it, I can 
change back.

+        if ( !iommu_intpost || !cap_intr_post(iommu->cap)
+            || !cpu_has_cx16 )
+            iommu_intpost = 0;


Thanks,
Feng

> 
> Jan


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