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Message-ID: <20231108235456.GB1132821@ls.amr.corp.intel.com>
Date: Wed, 8 Nov 2023 15:54:56 -0800
From: Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To: Jim Mattson <jmattson@...gle.com>
Cc: Isaku Yamahata <isaku.yamahata@...ux.intel.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,
Sean Christopherson <seanjc@...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 Tue, Nov 07, 2023 at 12:03:35PM -0800,
Jim Mattson <jmattson@...gle.com> wrote:
> On Tue, Nov 7, 2023 at 11:29 AM Isaku Yamahata
> <isaku.yamahata@...ux.intel.com> wrote:
> >
> > I meant bus clock frequency, not bus lock. Sorry for typo.
> >
> > On Tue, Nov 07, 2023 at 11:22:32AM -0800,
> > isaku.yamahata@...el.com wrote:
> >
> > > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > >
> > > Add KVM_CAP_X86_BUS_FREQUENCY_CONTROL capability to configure the core
> > > crystal clock (or processor's bus clock) for APIC timer emulation. Allow
> > > KVM_ENABLE_CAPABILITY(KVM_CAP_X86_BUS_FREUQNCY_CONTROL) to set the
> > > frequency. When using this capability, the user space VMM should configure
> > > CPUID[0x15] to advertise the frequency.
> > >
> > > TDX virtualizes CPUID[0x15] for the core crystal clock to be 25MHz. The
> > > x86 KVM hardcodes its freuqncy for APIC timer to be 1GHz. This mismatch
> > > causes the vAPIC timer to fire earlier than the guest expects. [1] The KVM
> > > APIC timer emulation uses hrtimer, whose unit is nanosecond.
> > >
> > > There are options to reconcile the mismatch. 1) Make apic bus clock frequency
> > > configurable (this patch). 2) TDX KVM code adjusts TMICT value. This is hacky
> > > and it results in losing MSB bits from 32 bit width to 30 bit width. 3). Make
> > > the guest kernel use tsc deadline timer instead of acpi oneshot/periodic timer.
> > > This is guest kernel choice. It's out of control of VMM.
> > >
> > > [1] https://lore.kernel.org/lkml/20231006011255.4163884-1-vannapurve@google.com/
> > >
> > > Isaku Yamahata (2):
> > > KVM: x86: Make the hardcoded APIC bus frequency vm variable
> > > KVM: X86: Add a capability to configure bus frequency for APIC timer
>
> 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()
- kselftest
Right now kvm kselftest doesn't have test cases even for in-kernel IRQCHIP
creation.
- Add test cases to create/destory in-kernel IRQCHIP
- Add KVM_ENABLE_CAPABILITY(KVM_CAP_X86_BUS_FREQUENCY_CONTROL) test cases
- Test if apic timer frequency is as spcified.
--
Isaku Yamahata <isaku.yamahata@...ux.intel.com>
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