linux-kernel - Re: [RFC PATCH v5 04/45] KVM: x86: Make "external SPTE" ops that can fail RET0 static calls

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Message-ID: <aYKd7qSExlJrbolH@google.com>
Date: Tue, 3 Feb 2026 17:16:30 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Rick P Edgecombe <rick.p.edgecombe@...el.com>
Cc: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>, Kai Huang <kai.huang@...el.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, Yan Y Zhao <yan.y.zhao@...el.com>, 
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kas@...nel.org" <kas@...nel.org>, 
	"mingo@...hat.com" <mingo@...hat.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>, 
	"binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>, 
	"ackerleytng@...gle.com" <ackerleytng@...gle.com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	"sagis@...gle.com" <sagis@...gle.com>, "tglx@...nel.org" <tglx@...nel.org>, "bp@...en8.de" <bp@...en8.de>, 
	Vishal Annapurve <vannapurve@...gle.com>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH v5 04/45] KVM: x86: Make "external SPTE" ops that can
 fail RET0 static calls

On Fri, Jan 30, 2026, Rick P Edgecombe wrote:
> On Thu, 2026-01-29 at 17:28 -0800, Sean Christopherson wrote:
> > 
> > Hmm, that's probably doable, but definitely in a separate patch. 
> > E.g. something
> > like:
> 
> I think it would be a good change. But after more consideration, I
> think the original patch is good on its own. Better to turn a bug into
> a deterministic thing, than an opportunity to consume stack. Seems to
> be what you intended.
> 
> Another idea would be to have a variant that returns an error instead
> of 0 so the callers can have there error logic triggered, but it's all
> incremental value on top of this.

I don't like that idea, at all.  First and foremost, I don't want to litter KVM
with WARNs for things that simply can't happen.  I'm fine adding infrastructure
that hides the sanity checks, but I don't want to bleed that into callers.

The other aspect I dislike is that returning a specific errno could lead to all
sorts of weirdness and hidden dependencies.

All in all, I think we'd be increasing the chances of creating bugs just to harden
against issues that in all likelihood will never happen.