linux-kernel - Re: [PATCH v15 09/13] tsc: Use the GUEST_TSC

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Message-ID: <a200bb73-9e6c-48a4-a123-372b7ec2baa9@amd.com>
Date: Tue, 17 Dec 2024 13:27:30 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Tom Lendacky <thomas.lendacky@....com>, linux-kernel@...r.kernel.org,
 bp@...en8.de, x86@...nel.org, kvm@...r.kernel.org
Cc: mingo@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com,
 pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v15 09/13] tsc: Use the GUEST_TSC_FREQ MSR for discovering
 TSC frequency

On 12/17/2024 12:35 PM, Tom Lendacky wrote:
> On 12/17/24 00:27, Nikunj A Dadhania wrote:
>> On 12/16/2024 10:01 PM, Tom Lendacky wrote:
>>> On 12/3/24 03:00, Nikunj A Dadhania wrote:
>>>> Calibrating the TSC frequency using the kvmclock is not correct for
>>>> SecureTSC enabled guests. Use the platform provided TSC frequency via the
>>>> GUEST_TSC_FREQ MSR (C001_0134h).
>>>>
>>>> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
>>>> ---
>>>>  arch/x86/include/asm/sev.h |  2 ++
>>>>  arch/x86/coco/sev/core.c   | 16 ++++++++++++++++
>>>>  arch/x86/kernel/tsc.c      |  5 +++++
>>>>  3 files changed, 23 insertions(+)
>>>>
> 
>> @@ -3282,16 +3283,18 @@ void __init snp_secure_tsc_prepare(void)
>>  
>>  static unsigned long securetsc_get_tsc_khz(void)
>>  {
>> -	unsigned long long tsc_freq_mhz;
>> -
>>  	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
> 
> I was thinking even this can be moved.

Yes, I am testing that out. If there is no dependency, I will move it.

Regards,
Nikunj