Re: [Xen-devel] [PATCH for-4.13] x86/passthrough: fix migration of MSI when using posted interrupts

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.10.2019 11:05, Roger Pau Monne wrote:
> @@ -411,6 +411,7 @@ int pt_irq_create_bind(
>  
>                  pirq_dpci->gmsi.gvec = pt_irq_bind->u.msi.gvec;
>                  pirq_dpci->gmsi.gflags = gflags;
> +                prev_vcpu_id = pirq_dpci->gmsi.dest_vcpu_id;

If this and ...

> @@ -440,7 +441,8 @@ int pt_irq_create_bind(
>          /* Use interrupt posting if it is supported. */
>          if ( iommu_intpost )
>              pi_update_irte(vcpu ? &vcpu->arch.hvm.vmx.pi_desc : NULL,
> -                           info, pirq_dpci->gmsi.gvec);
> +                           info, pirq_dpci->gmsi.gvec,
> +                           prev_vcpu_id >= 0 ? d->vcpu[prev_vcpu_id] : NULL);

... this are to be reliable, then - as explained to Joe already
in the earlier discussion - I think you need to update
pirq_dpci->gmsi.dest_vcpu_id in a code section a few lines up
from here (such that it would be reliable the next time we come
here) like this:

@@ -xxx,7 +yyy,10 @@
                 vcpu = vector_hashing_dest(d, dest, dest_mode,
                                            pirq_dpci->gmsi.gvec);
             if ( vcpu )
+            {
                 pirq_dpci->gmsi.posted = true;
+                pirq_dpci->gmsi.dest_vcpu_id = vcpu->vcpu_id;
+            }
         }
         if ( vcpu && is_iommu_enabled(d) )
             hvm_migrate_pirq(pirq_dpci, vcpu);

This ought to be fine because so far .dest_vcpu_id has a consumer
only in the non-posted case (in hvm_migrate_pirq()).

Considering that hvm_girq_dest_2_vcpu_id() isn't really inexpensive,
subsequent cleanup may then involve avoiding to call this function
if we'd overwrite .dest_vcpu_id as per above anyway.

> --- a/xen/drivers/passthrough/vtd/intremap.c
> +++ b/xen/drivers/passthrough/vtd/intremap.c
> @@ -946,12 +946,13 @@ void intel_iommu_disable_eim(void)
>          disable_qinval(drhd->iommu);
>  }
>  
> +#if CONFIG_HVM

#ifdef please.

Jan

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