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From: Thomas Gleixner <tglx@linutronix.de>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>, Sean Christopherson
 <seanjc@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>, X86 Kernel <x86@kernel.org>, Peter
 Zijlstra <peterz@infradead.org>, iommu@lists.linux.dev, Lu Baolu
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 robert.hoo.linux@gmail.com, jacob.jun.pan@linux.intel.com,
 oliver.sang@intel.com
Subject: Re: [PATCH v2 03/13] x86/irq: Remove bitfields in posted interrupt
 descriptor
In-Reply-To: <20240417110131.4aaf1d66@jacob-builder>
References: <20240405223110.1609888-1-jacob.jun.pan@linux.intel.com>
 <20240405223110.1609888-4-jacob.jun.pan@linux.intel.com>
 <Zh8aTitLwSYYlZW5@google.com> <20240417110131.4aaf1d66@jacob-builder>
Date: Thu, 18 Apr 2024 19:30:52 +0200
Message-ID: <87wmouy3w3.ffs@tglx>
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On Wed, Apr 17 2024 at 11:01, Jacob Pan wrote:
> On Tue, 16 Apr 2024 17:39:42 -0700, Sean Christopherson <seanjc@google.com>
> 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.