linux-kernel - Re: [PATCH v3 0/4] Allow AVIC's IPI virtualization to be optional

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Message-ID: <e5218efaceec20920166bd907416d6f88905558d.camel@redhat.com>
Date: Tue, 10 Sep 2024 16:13:07 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, Will Deacon <will@...nel.org>, 
 linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>, x86@...nel.org, Ingo Molnar
 <mingo@...hat.com>,  "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner
 <tglx@...utronix.de>, Joerg Roedel <joro@...tes.org>, Suravee Suthikulpanit
 <suravee.suthikulpanit@....com>,  Robin Murphy <robin.murphy@....com>,
 iommu@...ts.linux.dev, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 0/4] Allow AVIC's IPI virtualization to be optional

On Wed, 2023-10-04 at 16:14 +0300, Maxim Levitsky wrote:
> У пн, 2023-10-02 у 12:21 -0700, Sean Christopherson пише:
> > On Mon, Oct 02, 2023, Maxim Levitsky wrote:
> > > Hi!
> > > 
> > > This patch allows AVIC's ICR emulation to be optional and thus allows
> > > to workaround AVIC's errata #1235 by disabling this portion of the feature.
> > > 
> > > This is v3 of my patch series 'AVIC bugfixes and workarounds' including
> > > review feedback.
> > 
> > Please respond to my idea[*] instead of sending more patches. 
> 
> Hi,
> 
> For the v2 of the patch I was already on the fence if to do it this way or to refactor
> the code, and back when I posted it, I decided still to avoid the refactoring.
> 
> However, your idea of rewriting this patch, while it does change less lines of code,
> is even less obvious and consequently required you to write even longer comment to 
> justify it which is not a good sign.
> 
> In particular I don't want someone to find out later, and in the hard way that sometimes
> real physid table is accessed, and sometimes a fake copy of it is.
> 
> So I decided to fix the root cause by not reading the physid table back,
> which made the code cleaner, and even with the workaround the code 
> IMHO is still simpler than it was before.
> 
> About the added 'vcpu->loaded' variable, I added it also because it is something that is 
> long overdue to be added, I remember that in IPIv code there was also a need for this, 
> and probalby more places in KVM can be refactored to take advantage of it,
> instead of various hacks.
> 
> I did adopt your idea of using 'enable_ipiv', although I am still not 100% sure that this
> is more readable than 'avic_zen2_workaround'.

Hi!

Sean, can you take another look at this patch series?

Thanks in advance,
	Maxim Levitsky

> 
> Best regards,
> 	Maxim Levitsky
> 
> >  I'm not opposed to
> > a different approach, but we need to have an actual discussion around the pros and
> > cons, and hopefully come to an agreement.  This cover letter doesn't even acknowledge
> > that there is an alternative proposal, let alone justify why the vcpu->loaded
> > approach was taken.
> > 
> > [*] https://lore.kernel.org/all/ZRYxPNeq1rnp-M0f@google.com
> > 
> 
>