Re: [PATCH v2 03/13] x86/irq: Remove bitfields in posted interrupt descriptor

[Thomas Gleixner]

On Wed, Apr 17 2024 at 11:01, Jacob Pan wrote:
> On Tue, 16 Apr 2024 17:39:42 -0700, Sean Christopherson <seanjc@xxxxxxxxxx>
> wrote:
>> > diff --git a/arch/x86/kvm/vmx/posted_intr.c
>> > b/arch/x86/kvm/vmx/posted_intr.c index af662312fd07..592dbb765675 100644
>> > --- a/arch/x86/kvm/vmx/posted_intr.c
>> > +++ b/arch/x86/kvm/vmx/posted_intr.c
>> > @@ -107,7 +107,7 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int
>> > cpu)
>> >  		 * handle task migration (@cpu != vcpu->cpu).
>> >  		 */
>> >  		new.ndst = dest;
>> > -		new.sn = 0;
>> > +		new.notif_ctrl &= ~POSTED_INTR_SN;  
>> 
>> At the risk of creating confusing, would it make sense to add
>> double-underscore, non-atomic versions of the set/clear helpers for ON
>> and SN?
>> 
>> I can't tell if that's a net positive versus open coding clear() and
>> set() here and below.
> IMHO, we can add non-atomic helpers when we have more than one user for
> each operation.
>
> I do have a stupid bug here, it should be:
> -               new.notif_ctrl &= ~POSTED_INTR_SN;
> +               new.notif_ctrl &= ~BIT(POSTED_INTR_SN);

That's a perfect reason to use a proper helper.