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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan

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