Re: [RFC PATCH v2 65/69] KVM: X86: Introduce initial_tsc_khz in struct kvm_arch

[Paolo Bonzini]

On 03/07/21 00:05, isaku.yamahata@xxxxxxxxx wrote:
> From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
>
> 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@xxxxxxxxx>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
>   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);