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Message-ID: <20231107192933.GA1102144@ls.amr.corp.intel.com>
Date: Tue, 7 Nov 2023 11:29:33 -0800
From: Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To: isaku.yamahata@...el.com
Cc: 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>,
isaku.yamahata@...ux.intel.com
Subject: 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
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
>
> arch/x86/include/asm/kvm_host.h | 2 ++
> arch/x86/kvm/hyperv.c | 2 +-
> arch/x86/kvm/lapic.c | 6 ++++--
> arch/x86/kvm/lapic.h | 4 ++--
> arch/x86/kvm/x86.c | 16 ++++++++++++++++
> include/uapi/linux/kvm.h | 1 +
> 6 files changed, 26 insertions(+), 5 deletions(-)
>
> --
> 2.25.1
>
--
Isaku Yamahata <isaku.yamahata@...ux.intel.com>
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