linux-kernel - Re: [RFC PATCH v2 65/69] KVM: X86: Introduce initial_tsc_khz in struct kvm

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Message-ID: <YO3YDXLV7RQzMmXX@google.com>
Date:   Tue, 13 Jul 2021 18:14:37 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     isaku.yamahata@...el.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        isaku.yamahata@...il.com, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [RFC PATCH v2 65/69] KVM: X86: Introduce initial_tsc_khz in
 struct kvm_arch

On Tue, Jul 06, 2021, Paolo Bonzini wrote:
> On 03/07/21 00:05, isaku.yamahata@...el.com wrote:
> > From: Xiaoyao Li <xiaoyao.li@...el.com>
> > 
> > Introduce a per-vm variable initial_tsc_khz to hold the default tsc_khz
> > for kvm_arch_vcpu_create().
> > 
> > This field is going to be used by TDX since TSC frequency for TD guest
> > is configured at TD VM initialization phase.
> > 
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> >   arch/x86/include/asm/kvm_host.h | 1 +
> >   arch/x86/kvm/x86.c              | 3 ++-
> >   2 files changed, 3 insertions(+), 1 deletion(-)
> 
> So this means disabling TSC frequency scaling on TDX.  Would it make sense
> to delay VM creation to a separate ioctl, similar to KVM_ARM_VCPU_FINALIZE
> (KVM_VM_FINALIZE)?

There's an equivalent of that in the next mega-patch, the KVM_TDX_INIT_VM sub-ioctl
of KVM_MEMORY_ENCRYPT_OP.  The TSC frequency for the guest gets provided at that
time.