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Message-ID: <20231110002953.GB1102144@ls.amr.corp.intel.com>
Date: Thu, 9 Nov 2023 16:29:53 -0800
From: Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Isaku Yamahata <isaku.yamahata@...ux.intel.com>,
Jim Mattson <jmattson@...gle.com>, isaku.yamahata@...el.com,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
erdemaktas@...gle.com, Vishal Annapurve <vannapurve@...gle.com>
Subject: Re: KVM: X86: Make bus clock frequency for vapic timer (bus lock ->
bus clock) (was Re: [PATCH 0/2] KVM: X86: Make bus lock frequency for vapic
timer) configurable
On Thu, Nov 09, 2023 at 07:55:45AM -0800,
Sean Christopherson <seanjc@...gle.com> wrote:
> On Wed, Nov 08, 2023, Isaku Yamahata wrote:
> > On Tue, Nov 07, 2023 at 12:03:35PM -0800, Jim Mattson <jmattson@...gle.com> wrote:
> > > I think I know the answer, but do you have any tests for this new feature?
> >
> > If you mean kvm kselftest, no.
> > I have
> > - TDX patched qemu
> > - kvm-unit-tests: test_apic_timer_one_shot() @ kvm-unit-tests/x86/apic.c
> > TDX version is found at https://github.com/intel/kvm-unit-tests-tdx
> > We're planning to upstream the changes for TDX
> >
> > How far do we want to go?
> > - Run kvm-unit-tests with TDX. What I have right now.
> > - kvm-unit-tests: extend qemu for default VM case and update
> > test_apic_timer_one_host()
>
> Hrm, I'm not sure that we can do a whole lot for test_apic_timer_one_shot(). Or
> rather, I'm not sure it's worth the effort to try and add coverage beyond what's
> already there.
>
> As for TDX, *if* we extend KUT, please don't make it depend on TDX. Very few people
> have access to TDX platforms and anything CoCo is pretty much guaranteed to be harder
> to debug.
It made the test cases work with TDX + UEFI bios by adjusting command line to
invoke qemu. And skip unsuitable tests.
Maybe we can generalize the way to twist qemu command line.
> > - kselftest
> > Right now kvm kselftest doesn't have test cases even for in-kernel IRQCHIP
> > creation.
>
> Selftests always create an in-kernel APIC. And I think selftests are perfectly
> suited to complement the coverage provided by KUT. Specifically, the failure
> scenario for this is that KVM emulates at 1Ghz whereas TDX advertises 25Mhz, i.e.
> the test case we want is to verify that the APIC timer doesn't expire early.
>
> There's no need for any APIC infrastructure, e.g. a selftest doesn't even need to
> handle an interrupt. Get the TSC frequency from KVM, program up an arbitrary APIC
> bus clock frequency, set TMICT such that it expires waaaay in the future, and then
> verify that the APIC timer counts reasonably close to the programmed frequency.
> E.g. if the test sets the bus clock to 25Mhz, the "drift" due to KVM counting at
> 1Ghz should be super obvious.
Oh, only check the register value without interrupt. Good idea. Let me give it
a try.
--
Isaku Yamahata <isaku.yamahata@...ux.intel.com>
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