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Date:   Mon, 5 Dec 2022 11:23:32 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Kim Phillips <kim.phillips@amd.com>
Cc:     x86@kernel.org, Babu Moger <Babu.Moger@amd.com>,
        Borislav Petkov <bp@suse.de>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Joao Martins <joao.m.martins@oracle.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Tony Luck <tony.luck@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Alexey Kardashevskiy <aik@amd.com>, kvm@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/7] x86/cpu: Define a scattered No Nested Data
 Breakpoints feature bit
Message-ID: <Y43GpD9fgnOGNEcu@zn.tnic>
References: <20221201015003.295769-1-kim.phillips@amd.com>
 <20221201015003.295769-2-kim.phillips@amd.com>
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On Wed, Nov 30, 2022 at 07:49:57PM -0600, Kim Phillips wrote:
> It's a part of the CPUID 0x80000021 leaf, and this allows us to
							    ^^

Please use passive voice in your commit message: no "we" or "I", etc,
and describe your changes in imperative mood.

Personal pronouns are ambiguous in text, especially with so many
parties/companies/etc developing the kernel so let's avoid them please.

> group this and other CPUID 0x80000021 EAX feature bits to being
> propagated via kvm_set_cpu_caps instead of open-coding them in
> __do_cpuid_func().
> 
> Signed-off-by: Kim Phillips <kim.phillips@amd.com>
> ---
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  arch/x86/kernel/cpu/scattered.c    | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 11a0e06362e4..b16fdcedc2b5 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -307,6 +307,7 @@
>  #define X86_FEATURE_SGX_EDECCSSA	(11*32+18) /* "" SGX EDECCSSA user leaf function */
>  #define X86_FEATURE_CALL_DEPTH		(11*32+19) /* "" Call depth tracking for RSB stuffing */
>  #define X86_FEATURE_MSR_TSX_CTRL	(11*32+20) /* "" MSR IA32_TSX_CTRL (Intel) implemented */
> +#define X86_FEATURE_NO_NESTED_DATA_BP	(11*32+21) /* "" AMD No Nested Data Breakpoints */

Right, what is the use of this bit in a KVM guest? Running perf tool in
a guest would use that bit how?

Thx.

-- 
Regards/Gruss,
    Boris.

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