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

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Date:   Tue, 6 Jul 2021 16:22:04 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     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>,
        Sean Christopherson <seanjc@...gle.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     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 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)?

Paolo

> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index a47e17892258..ae8b96e15e71 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1030,6 +1030,7 @@ struct kvm_arch {
>   	u64 last_tsc_nsec;
>   	u64 last_tsc_write;
>   	u32 last_tsc_khz;
> +	u32 initial_tsc_khz;
>   	u64 cur_tsc_nsec;
>   	u64 cur_tsc_write;
>   	u64 cur_tsc_offset;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a8299add443f..d3ebed784eac 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10441,7 +10441,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>   	else
>   		vcpu->arch.mp_state = KVM_MP_STATE_UNINITIALIZED;
>   
> -	kvm_set_tsc_khz(vcpu, max_tsc_khz);
> +	kvm_set_tsc_khz(vcpu, vcpu->kvm->arch.initial_tsc_khz);
>   
>   	r = kvm_mmu_create(vcpu);
>   	if (r < 0)
> @@ -10894,6 +10894,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>   	pvclock_update_vm_gtod_copy(kvm);
>   
>   	kvm->arch.guest_can_read_msr_platform_info = true;
> +	kvm->arch.initial_tsc_khz = max_tsc_khz;
>   
>   	INIT_DELAYED_WORK(&kvm->arch.kvmclock_update_work, kvmclock_update_fn);
>   	INIT_DELAYED_WORK(&kvm->arch.kvmclock_sync_work, kvmclock_sync_fn);
>