linux-kernel - Re: [PATCH v11 20/20] x86/cpu/amd: Do not print FW

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Message-ID: <7fe54097-20d8-fb9c-e79d-b62910b50154@amd.com>
Date: Mon, 16 Sep 2024 17:10:48 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Jim Mattson <jmattson@...gle.com>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, bp@...en8.de,
 x86@...nel.org, kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
 dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com,
 pbonzini@...hat.com
Subject: Re: [PATCH v11 20/20] x86/cpu/amd: Do not print FW_BUG for Secure TSC



On 9/13/2024 11:12 PM, Jim Mattson wrote:
> On Wed, Jul 31, 2024 at 8:16 AM Nikunj A Dadhania <nikunj@....com> wrote:
>>
>> When Secure TSC is enabled and TscInvariant (bit 8) in CPUID_8000_0007_edx
>> is set, the kernel complains with the below firmware bug:
>>
>> [Firmware Bug]: TSC doesn't count with P0 frequency!
>>
>> Secure TSC does not need to run at P0 frequency; the TSC frequency is set
>> by the VMM as part of the SNP_LAUNCH_START command. Skip this check when
>> Secure TSC is enabled
>>
>> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
>> Tested-by: Peter Gonda <pgonda@...gle.com>
>> ---
>>  arch/x86/kernel/cpu/amd.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
>> index be5889bded49..87b55d2183a0 100644
>> --- a/arch/x86/kernel/cpu/amd.c
>> +++ b/arch/x86/kernel/cpu/amd.c
>> @@ -370,7 +370,8 @@ static void bsp_determine_snp(struct cpuinfo_x86 *c)
>>
>>  static void bsp_init_amd(struct cpuinfo_x86 *c)
>>  {
>> -       if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
>> +       if (cpu_has(c, X86_FEATURE_CONSTANT_TSC) &&
>> +           !cc_platform_has(CC_ATTR_GUEST_SECURE_TSC)) {
> 
> Could we extend this to never complain in a virtual machine? i.e.

Let me get more clarity on the below and your commit[1]

> ...
> -       if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
> +       if (cpu_has(c, X86_FEATURE_CONSTANT_TSC) &&
> +           !cpu_has(c, X86_FEATURE_HYPERVISOR)) {
> ...

Or do this for Family 15h and above ?

Regards
Nikunj

1. https://github.com/torvalds/linux/commit/8b0e00fba934