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Message-ID: <Y6rOTM6Q7AZekpoc@zn.tnic>
Date: Tue, 27 Dec 2022 11:51:56 +0100
From: Borislav Petkov <bp@...en8.de>
To: Kim Phillips <kim.phillips@....com>
Cc: x86@...nel.org, Babu Moger <Babu.Moger@....com>,
Borislav Petkov <bp@....com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
Joao Martins <joao.m.martins@...cle.com>,
Jonathan Corbet <corbet@....net>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>,
David Woodhouse <dwmw@...zon.co.uk>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Juergen Gross <jgross@...e.com>,
Peter Zijlstra <peterz@...radead.org>,
Tony Luck <tony.luck@...el.com>,
Tom Lendacky <thomas.lendacky@....com>,
Alexey Kardashevskiy <aik@....com>, kvm@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/7] x86/cpu: Make X86_FEATURE_LFENCE_RDTSC a
scattered feature bit
On Mon, Dec 05, 2022 at 05:32:31PM -0600, Kim Phillips wrote:
> It's a part of the CPUID 0x80000021 leaf, and will be grouped
> with other feature bits to being propagated via kvm_set_cpu_caps()
> instead of open-coding them in __do_cpuid_func().
>
> Unlike the other CPUID 0x80000021 EAX feature bits,
> X86_FEATURE_LFENCE_RDTSC already had an entry in cpufeatures.h.
>
> Signed-off-by: Kim Phillips <kim.phillips@....com>
> ---
> arch/x86/kernel/cpu/scattered.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
> index d0734cc19d37..caa03466cd9e 100644
> --- a/arch/x86/kernel/cpu/scattered.c
> +++ b/arch/x86/kernel/cpu/scattered.c
> @@ -46,6 +46,7 @@ static const struct cpuid_bit cpuid_bits[] = {
> { X86_FEATURE_PROC_FEEDBACK, CPUID_EDX, 11, 0x80000007, 0 },
> { X86_FEATURE_MBA, CPUID_EBX, 6, 0x80000008, 0 },
> { X86_FEATURE_NO_NESTED_DATA_BP,CPUID_EAX, 0, 0x80000021, 0 },
> + { X86_FEATURE_LFENCE_RDTSC, CPUID_EAX, 2, 0x80000021, 0 },
Hmm, so this patchset keeps growing and growing with new bits.
Perhaps my initial suggestion to make it a scattered one doesn't make
a whole lot of sense anymore.
/me goes and looks at CPUID_Fn80000021_EAX [Extended Feature 2 EAX] (Core::X86::Cpuid::FeatureExt2Eax)
Yah, judging by what's there in that leaf, we are likely to use a lot
more bits in the future I think you should go back to
https://lore.kernel.org/lkml/20221104213651.141057-2-kim.phillips@amd.com/
But please state in that commit message that the majority of the feature
bits in CPUID_Fn80000021_EAX will be used in the kernel and thus a
separate leaf makes sense.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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