Re: [PATCH 7/8] KVM: VMX: Expose TSC scaling to L2

From: Maxim Levitsky <mlevitsk@redhat.com>
To: ilstam@mailbox.org, kvm@vger.kernel.org, pbonzini@redhat.com
Cc: ilstam@amazon.com, seanjc@google.com, vkuznets@redhat.com,
	wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org,
	haozhong.zhang@intel.com, zamsden@gmail.com, mtosatti@redhat.com,
	dplotnikov@virtuozzo.com, dwmw@amazon.co.uk
Subject: Re: [PATCH 7/8] KVM: VMX: Expose TSC scaling to L2
Date: Mon, 10 May 2021 16:56:38 +0300	[thread overview]
Message-ID: <a6bb045bde7068c29a9103ccada57076bb39bd50.camel@redhat.com> (raw)
In-Reply-To: <20210506103228.67864-8-ilstam@mailbox.org>

On Thu, 2021-05-06 at 10:32 +0000, ilstam@mailbox.org wrote:
> From: Ilias Stamatis <ilstam@amazon.com>
> 
> Expose the TSC scaling feature to nested guests.
> 
> Signed-off-by: Ilias Stamatis <ilstam@amazon.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index a1bf28f33837..639cb9462103 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2277,7 +2277,8 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
>  				  SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE |
>  				  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
>  				  SECONDARY_EXEC_APIC_REGISTER_VIRT |
> -				  SECONDARY_EXEC_ENABLE_VMFUNC);
> +				  SECONDARY_EXEC_ENABLE_VMFUNC |
> +				  SECONDARY_EXEC_TSC_SCALING);
>  		if (nested_cpu_has(vmcs12,
>  				   CPU_BASED_ACTIVATE_SECONDARY_CONTROLS))
>  			exec_control |= vmcs12->secondary_vm_exec_control;
> @@ -6483,7 +6484,8 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
>  		SECONDARY_EXEC_RDRAND_EXITING |
>  		SECONDARY_EXEC_ENABLE_INVPCID |
>  		SECONDARY_EXEC_RDSEED_EXITING |
> -		SECONDARY_EXEC_XSAVES;
> +		SECONDARY_EXEC_XSAVES |
> +		SECONDARY_EXEC_TSC_SCALING;
>  
>  	/*
>  	 * We can emulate "VMCS shadowing," even if the hardware

Seems to be correct. I don't yet have experience with how VMX does the VMX capablity
msrs and primary/secondary/entry/exit/pinbased control fitering for features that are not supported on the host,
but after digging through it this seems to be OK.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky