linux-kernel - Re: [RFC PATCH 0/6] KVM: x86: async PF user

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Message-ID: <Z8D5d85N3LJBJ2LD@google.com>
Date: Thu, 27 Feb 2025 15:47:03 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Nikita Kalyazin <kalyazin@...zon.com>
Cc: pbonzini@...hat.com, corbet@....net, tglx@...utronix.de, mingo@...hat.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, rostedt@...dmis.org, 
	mhiramat@...nel.org, mathieu.desnoyers@...icios.com, kvm@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
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	graf@...zon.de, jgowans@...zon.com, roypat@...zon.co.uk, derekmn@...zon.com, 
	nsaenz@...zon.es, xmarcalx@...zon.com
Subject: Re: [RFC PATCH 0/6] KVM: x86: async PF user

On Thu, Feb 27, 2025, Nikita Kalyazin wrote:
> On 27/02/2025 16:44, Sean Christopherson wrote:
> > When it comes to uAPI, I want to try and avoid statements along the lines of
> > "IF 'x' holds true, then 'y' SHOULDN'T be a problem".  If this didn't impact uAPI,
> > I wouldn't care as much, i.e. I'd be much more willing iterate as needed.
> > 
> > I'm not saying we should go straight for a complex implementation.  Quite the
> > opposite.  But I do want us to consider the possible ramifications of using a
> > single bit for all userfaults, so that we can at least try to design something
> > that is extensible and won't be a pain to maintain.
> 
> So you would've liked more the "two-bit per gfn" approach as in: provide 2
> interception points, for sync and async exits, with the former chosen by
> userspace when it "knows" that the content is already in memory? 

No, all I'm saying is I want people think about what the future will look like,
to minimize the chances of ending up with a mess.