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: <Z6uIGwxx9HzZQ-N7@google.com>
Date: Tue, 11 Feb 2025 09:25:47 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Borislav Petkov <bp@...en8.de>
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 Tue, Feb 11, 2025, Borislav Petkov wrote:
> 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?

Because obviously optimizing code that's called once during boot is super
critical?

> 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?

Ah, yeah, that's way better.