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Message-ID: <ZXswR04H9Tl7xlyj@google.com>
Date: Thu, 14 Dec 2023 08:41:43 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Maxim Levitsky <mlevitsk@...hat.com>
Cc: 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>,
Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v2 1/3] KVM: x86: Make the hardcoded APIC bus frequency vm variable
On Thu, Dec 14, 2023, Maxim Levitsky wrote:
> On Wed, 2023-12-13 at 15:10 -0800, Sean Christopherson wrote:
> > Upstream KVM's non-TDX behavior is fine, because KVM doesn't advertise support
> > for CPUID 0x15, i.e. doesn't announce to host userspace that it's safe to expose
> > CPUID 0x15 to the guest. Because TDX makes exposing CPUID 0x15 mandatory, KVM
> > needs to be taught to correctly emulate the guest's APIC bus frequency, a.k.a.
> > the TDX guest core crystal frequency of 25Mhz.
>
> I assume that TDX doesn't allow to change the CPUID 0x15 leaf.
Correct. I meant to call that out below, but left my sentence half-finished. It
was supposed to say:
I halfheartedly floated the idea of "fixing" the TDX module/architecture to either
use 1Ghz as the base frequency or to allow configuring the base frequency
advertised to the guest.
> > I halfheartedly floated the idea of "fixing" the TDX module/architecture to either
> > use 1Ghz as the base frequency (off list), but it definitely isn't a hill worth
> > dying on since the KVM changes are relatively simple.
> >
> > https://lore.kernel.org/all/ZSnIKQ4bUavAtBz6@google.com
> >
>
> Best regards,
> Maxim Levitsky
>
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