Re: [Xen-devel] [PATCH for-4.13 v3 2/2] x86/vmx: always sync PIR to IRR before vmentry

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Nov 27, 2019 at 12:30:06PM +0100, Jan Beulich wrote:
> On 27.11.2019 12:22, Roger Pau Monné  wrote:
> > On Tue, Nov 26, 2019 at 05:50:32PM +0100, Jan Beulich wrote:
> >> On 26.11.2019 14:26, Roger Pau Monne wrote:
> >>> --- a/xen/arch/x86/hvm/irq.c
> >>> +++ b/xen/arch/x86/hvm/irq.c
> >>> @@ -515,7 +515,11 @@ void hvm_set_callback_via(struct domain *d, uint64_t 
> >>> via)
> >>>  struct hvm_intack hvm_vcpu_has_pending_irq(struct vcpu *v)
> >>>  {
> >>>      struct hvm_domain *plat = &v->domain->arch.hvm;
> >>> -    int vector;
> >>> +    /*
> >>> +     * Always call vlapic_has_pending_irq so that PIR is synced into IRR 
> >>> when
> >>> +     * using posted interrupts.
> >>> +     */
> >>> +    int vector = vlapic_has_pending_irq(v);
> >>
> >> Did you consider doing this conditionally either here ...
> >>
> >>> @@ -530,7 +534,6 @@ struct hvm_intack hvm_vcpu_has_pending_irq(struct 
> >>> vcpu *v)
> >>>      if ( vlapic_accept_pic_intr(v) && plat->vpic[0].int_output )
> >>>          return hvm_intack_pic(0);
> >>>  
> >>> -    vector = vlapic_has_pending_irq(v);
> >>>      if ( vector != -1 )
> >>>          return hvm_intack_lapic(vector);
> >>
> >> ... or here?
> > 
> > I'm afraid I don't follow. The whole point of this change is to ensure
> > vlapic_has_pending_irq is unconditionally called in
> > hvm_vcpu_has_pending_irq, so I'm not sure what you mean by "doing this
> > conditionally...".
> 
> Do it early when using interrupt posting, and keep it in its
> current place otherwise.
> 
> >> I ask not only because the function isn't exactly
> >> cheap to call (as iirc you did also mention during the v2
> >> discussion), but also because of its interaction with Viridian
> >> and nested mode. In case of problems there, avoiding the use
> >> of interrupt posting would be a workaround in such cases then.
> > 
> > Would you like me to export something like vlapic_sync_pir_to_irr and
> > call it unconditionally instead of calling vlapic_has_pending_irq?
> 
> This looks to be another option, yes. Albeit instead of making
> non-static (which I assume is what you mean by "export"), maybe
> simply make this a static inline in vlapic.h then.

Yes, that would work and IMO is better than moving the call to
vlapic_has_pending_irq around. Are you OK with this approach?

Thanks, Roger.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel