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 14:20:54 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Rick P Edgecombe
	<rick.p.edgecombe@...el.com>
CC: "jmattson@...gle.com" <jmattson@...gle.com>, Chao Gao
	<chao.gao@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "vkuznets@...hat.com" <vkuznets@...hat.com>,
	Vishal Annapurve <vannapurve@...gle.com>, Xiaoyao Li <xiaoyao.li@...el.com>,
	Erdem Aktas <erdemaktas@...gle.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "mlevitsk@...hat.com" <mlevitsk@...hat.com>, "Isaku
 Yamahata" <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

Hi Sean,

On 4/24/2024 10:23 AM, Sean Christopherson wrote:
> On Wed, Apr 24, 2024, Rick P Edgecombe wrote:
>> 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.
> 
> I have no problem posting "early", but Documentation/process/maintainer-kvm-x86.rst
> clearly states under Testing that:
> 
>   If you can't fully test a change, e.g. due to lack of hardware, clearly state
>   what level of testing you were able to do, e.g. in the cover letter.
> 
> I was assuming that this was actually *fully* tested, because nothing suggests
> otherwise.  And _that_ is a problem, e.g. I was planning on applying this series
> for 6.10, which would have made for quite the mess if it turns out that this
> doesn't actually solve the TDX problem.

There was one vote for the capability name to rather be KVM_CAP_X86_APIC_BUS_CYCLES_NS [1] 

I'd be happy to resubmit with the name changed but after reading your statement above it
is not clear to me what name is preferred: KVM_CAP_X86_APIC_BUS_FREQUENCY
as used in this series that seem to meet your approval or KVM_CAP_X86_APIC_BUS_CYCLES_NS.

Please let me know what you prefer.

Thank you.

Reinette

[1] https://lore.kernel.org/lkml/1e26b405-f382-45f4-9dd5-3ea5db68302a@intel.com/