linux-kernel - Re: [PATCH v2 1/2] x86/cpufeatures: Add virtual TSC

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Date:   Wed, 20 Apr 2022 13:43:22 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Babu Moger <babu.moger@....com>
Cc:     tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, jmattson@...gle.com, joro@...tes.org,
        wanpengli@...cent.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 1/2] x86/cpufeatures: Add virtual TSC_AUX feature bit

On Tue, Apr 19, 2022 at 03:53:52PM -0500, Babu Moger wrote:
> The TSC_AUX Virtualization feature allows AMD SEV-ES guests to securely use
> TSC_AUX (auxiliary time stamp counter data) MSR in RDTSCP and RDPID
> instructions.
> 
> The TSC_AUX MSR is typically initialized to APIC ID or another unique
> identifier so that software can quickly associate returned TSC value
> with the logical processor.
> 
> Add the feature bit and also include it in the kvm for detection.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> Acked-by: Borislav Petkov <bp@...e.de>
> ---
> v2:
> Fixed the text(commented by Boris).
> Added Acked-by from Boris.
> 
> v1:
> https://lore.kernel.org/kvm/164937947020.1047063.14919887750944564032.stgit@bmoger-ubuntu/
> 
>  arch/x86/include/asm/cpufeatures.h |    1 +
>  arch/x86/kvm/cpuid.c               |    2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 73e643ae94b6..1bc66a17a95a 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -405,6 +405,7 @@
>  #define X86_FEATURE_SEV			(19*32+ 1) /* AMD Secure Encrypted Virtualization */
>  #define X86_FEATURE_VM_PAGE_FLUSH	(19*32+ 2) /* "" VM Page Flush MSR is supported */
>  #define X86_FEATURE_SEV_ES		(19*32+ 3) /* AMD Secure Encrypted Virtualization - Encrypted State */
> +#define X86_FEATURE_V_TSC_AUX		(19*32+ 9) /* Virtual TSC_AUX */

I forgot from the last time: nothing is going to use that bit in
userspace so make that

#define X86_FEATURE_V_TSC_AUX		(19*32+ 9) /* "" Virtual TSC_AUX */

please.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette