linux-kernel - Re: [PATCH V4 0/4] KVM: x86: Make bus clock frequency for vAPIC timer configurable

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Date: Wed, 24 Apr 2024 16:38:52 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>
CC: "jmattson@...gle.com" <jmattson@...gle.com>, "Gao, Chao"
	<chao.gao@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "vkuznets@...hat.com" <vkuznets@...hat.com>,
	"Annapurve, Vishal" <vannapurve@...gle.com>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "Chatre, Reinette" <reinette.chatre@...el.com>,
	"Aktas, Erdem" <erdemaktas@...gle.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "mlevitsk@...hat.com" <mlevitsk@...hat.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>
Subject: Re: [PATCH V4 0/4] KVM: x86: Make bus clock frequency for vAPIC timer
 configurable

On Wed, 2024-04-24 at 09:13 -0700, Sean Christopherson wrote:
> On Tue, Apr 16, 2024, Rick P Edgecombe wrote:
> > On Thu, 2024-03-21 at 09:37 -0700, Reinette Chatre wrote:
> > > 
> > > Summary
> > > -------
> > > Add KVM_CAP_X86_APIC_BUS_FREQUENCY capability to configure the APIC
> > > bus clock frequency for APIC timer emulation.
> > > Allow KVM_ENABLE_CAPABILITY(KVM_CAP_X86_APIC_BUS_FREQUENCY) to set the
> > > frequency in nanoseconds. When using this capability, the user space
> > > VMM should configure CPUID leaf 0x15 to advertise the frequency.
> > 
> > Looks good to me and...
> > Tested-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> > 
> > The only thing missing is actually integrating it into TDX qemu patches and
> > testing the resulting TD. I think we are making a fair assumption that the
> > problem should be resolved based on the analysis, but we have not actually
> > tested that part. Is that right?
> 
> Please tell me that Rick is wrong, and that this actually has been tested with
> a TDX guest.  I don't care _who_ tested it, or with what VMM it has been
> tested,
> but _someone_ needs to verify that this actually fixes the TDX issue.

It is in the process of getting a TDX test developed (or rather updated).
Agreed, it requires verification that it fixes the original TDX issue. That is
why I raised it.

Reinette was working on this internally and some iterations were happening, but
we are trying to work on the public list as much as possible per your earlier
comments. So that is why she posted it.

There was at least some level of TDX integration in the past. I'm not sure what
exactly was tested, but we are going to re-verify it with the latest everything.