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

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Message-ID: <ZvE06wB0JGWXGxpK@google.com>
Date: Mon, 23 Sep 2024 02:29:55 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Maxim Levitsky <mlevitsk@...hat.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 Tue, Sep 10, 2024, Maxim Levitsky wrote:
> 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?

Ya, it might take a week or two, but it's on my todo list.