linux-kernel - Re: [PATCH 01/16] x86/tsc: Add a standalone helpers for getting TSC info from CPUID.0x15

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Message-ID: <20250211150114.GCZ6tmOqV4rI04HVuY@fat_crate.local>
Date: Tue, 11 Feb 2025 16:01:14 +0100
From: Borislav Petkov <bp@...en8.de>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Juergen Gross <jgross@...e.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Ajay Kaher <ajay.kaher@...adcom.com>,
	Alexey Makhalov <alexey.amakhalov@...adcom.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
	linux-coco@...ts.linux.dev, virtualization@...ts.linux.dev,
	linux-hyperv@...r.kernel.org, jailhouse-dev@...glegroups.com,
	kvm@...r.kernel.org, xen-devel@...ts.xenproject.org,
	Nikunj A Dadhania <nikunj@....com>,
	Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 01/16] x86/tsc: Add a standalone helpers for getting TSC
 info from CPUID.0x15

On Fri, Jan 31, 2025 at 06:17:03PM -0800, Sean Christopherson wrote:
> Extract retrieval of TSC frequency information from CPUID into standalone
> helpers so that TDX guest support and kvmlock can reuse the logic.  Provide
> a version that includes the multiplier math as TDX in particular does NOT
> want to use native_calibrate_tsc()'s fallback logic that derives the TSC
> frequency based on CPUID.0x16 when the core crystal frequency isn't known.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/include/asm/tsc.h | 41 ++++++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/tsc.c      | 14 ++-----------
>  2 files changed, 43 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
> index 94408a784c8e..14a81a66b37c 100644
> --- a/arch/x86/include/asm/tsc.h
> +++ b/arch/x86/include/asm/tsc.h

Bah, why in the header as inlines? Just leave them in tsc.c and call them...

> @@ -28,6 +28,47 @@ static inline cycles_t get_cycles(void)
>  }
>  #define get_cycles get_cycles
>  
> +static inline int cpuid_get_tsc_info(unsigned int *crystal_khz,
> +				     unsigned int *denominator,
> +				     unsigned int *numerator)

Can we pls do a

struct cpuid_tsc_info {
	unsigned int denominator;
	unsigned int numerator;
	unsigned int crystal_khz;
	unsigned int tsc_khz;
}

and hand that around instead of those I/O pointers?

It would make the code a bit saner to stare at and follow.

Thx.

-- 
Regards/Gruss,
    Boris.

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