linux-kernel - Re: [PATCH v2 09/11] x86/kvmclock: Use Secure TSC as clock if available

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Date:   Mon, 3 Apr 2023 16:45:17 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc:     bp@...en8.de, dionnaglaze@...gle.com, pgonda@...gle.com,
        seanjc@...gle.com, pbonzini@...hat.com, michael.roth@....com,
        ketanch@...k.ac.in
Subject: Re: [PATCH v2 09/11] x86/kvmclock: Use Secure TSC as clock if
 available

On 3/26/23 09:46, Nikunj A Dadhania wrote:
> For AMD SNP guests having Secure TSC enabled, use Secure TSC based
> clocksource instead of kvmclock.

This patch only results in skipping the initialization of KVM clock, it 
doesn't cause Secure TSC to be used as the clocksource.

Thanks,
Tom

> 
> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
> ---
>   arch/x86/kernel/kvmclock.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index 0f35d44c56fe..1be342064851 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -288,7 +288,7 @@ void __init kvmclock_init(void)
>   {
>   	u8 flags;
>   
> -	if (!kvm_para_available() || !kvmclock)
> +	if (!kvm_para_available() || !kvmclock || cc_platform_has(CC_ATTR_GUEST_SECURE_TSC))
>   		return;
>   
>   	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {