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

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Date:   Mon, 26 Jul 2021 13:31:21 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     "Yamahata, Isaku" <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" <erdemaktas@...gle.com>,
        Connor Kuehl <ckuehl@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>
Subject: Re: [RFC PATCH v2 65/69] KVM: X86: Introduce initial_tsc_khz in
 struct kvm_arch

On 7/14/2021 2:14 AM, Sean Christopherson wrote:
> 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.  

No. It still supports TSC frequency scaling on TDX. Only that we need to 
configure TSC frequency for TD guest at VM level, not vcpu level.

>> 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.
>