linux-kernel - Re: [PATCH v5 13/14] x86/tsc: Mark Secure TSC as reliable clocksource

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Message-ID: <ae267e31-5722-4784-9146-28bb13ca7cf5@amd.com>
Date:   Thu, 2 Nov 2023 11:23:34 +0530
From:   "Nikunj A. Dadhania" <nikunj@....com>
To:     Dave Hansen <dave.hansen@...el.com>, linux-kernel@...r.kernel.org,
        thomas.lendacky@....com, x86@...nel.org, kvm@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     bp@...en8.de, mingo@...hat.com, tglx@...utronix.de,
        dave.hansen@...ux.intel.com, dionnaglaze@...gle.com,
        pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v5 13/14] x86/tsc: Mark Secure TSC as reliable clocksource

On 10/30/2023 10:48 PM, Dave Hansen wrote:
> On 10/29/23 23:36, Nikunj A Dadhania wrote:
> ...
>> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
>> index 15f97c0abc9d..b0a8546d3703 100644
>> --- a/arch/x86/kernel/tsc.c
>> +++ b/arch/x86/kernel/tsc.c
>> @@ -1241,7 +1241,7 @@ static void __init check_system_tsc_reliable(void)
>>  			tsc_clocksource_reliable = 1;
>>  	}
>>  #endif
>> -	if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
>> +	if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE) || cc_platform_has(CC_ATTR_GUEST_SECURE_TSC))
>>  		tsc_clocksource_reliable = 1;
> 
> Why can't you just set X86_FEATURE_TSC_RELIABLE?

Last time when I tried, I had removed my kvmclock changes and I had set the X86_FEATURE_TSC_RELIABLE similar to Kirill's patch[1], this did not select the SecureTSC.

Let me try setting X86_FEATURE_TSC_RELIABLE and retaining my patch for skipping kvmclock.

Regards
Nikunj

1: https://lore.kernel.org/lkml/20230808162320.27297-1-kirill.shutemov@linux.intel.com/