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

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Date: Thu, 18 Apr 2024 11:10:24 -0700
From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Sean Christopherson <seanjc@...gle.com>, LKML
 <linux-kernel@...r.kernel.org>, X86 Kernel <x86@...nel.org>, Peter Zijlstra
 <peterz@...radead.org>, iommu@...ts.linux.dev, Lu Baolu
 <baolu.lu@...ux.intel.com>, kvm@...r.kernel.org, Dave Hansen
 <dave.hansen@...el.com>, Joerg Roedel <joro@...tes.org>, "H. Peter Anvin"
 <hpa@...or.com>, Borislav Petkov <bp@...en8.de>, Ingo Molnar
 <mingo@...hat.com>, Paul Luse <paul.e.luse@...el.com>, Dan Williams
 <dan.j.williams@...el.com>, Jens Axboe <axboe@...nel.dk>, Raj Ashok
 <ashok.raj@...el.com>, Kevin Tian <kevin.tian@...el.com>, maz@...nel.org,
 Robin Murphy <robin.murphy@....com>, jim.harris@...sung.com,
 a.manzanares@...sung.com, Bjorn Helgaas <helgaas@...nel.org>,
 guang.zeng@...el.com, robert.hoo.linux@...il.com, oliver.sang@...el.com,
 jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 03/13] x86/irq: Remove bitfields in posted interrupt
 descriptor

Hi Thomas,

On Thu, 18 Apr 2024 19:30:52 +0200, Thomas Gleixner <tglx@...utronix.de>
wrote:

> On Wed, Apr 17 2024 at 11:01, Jacob Pan wrote:
> > On Tue, 16 Apr 2024 17:39:42 -0700, Sean Christopherson
> > <seanjc@...gle.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.
I just proved I was wrong:) will do.

Thanks,

Jacob