linux-kernel - Re: [PATCH v2 1/2] x86/cpu, kvm: Use CPU capabilities for CPUID[0x80000021].EAX

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Date:   Thu, 24 Nov 2022 14:06:23 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Kim Phillips <kim.phillips@....com>
Cc:     x86@...nel.org, Babu Moger <Babu.Moger@....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>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] x86/cpu, kvm: Use CPU capabilities for
 CPUID[0x80000021].EAX

On Wed, Nov 23, 2022 at 06:04:48PM -0600, Kim Phillips wrote:
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index c92c49a0b35b..61cd33a848cc 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -730,6 +730,25 @@ void kvm_set_cpu_caps(void)
>  		0 /* SME */ | F(SEV) | 0 /* VM_PAGE_FLUSH */ | F(SEV_ES) |
>  		F(SME_COHERENT));
>  
> +	/*
> +	 * Pass down these bits:
> +	 *    EAX      0      NNDBP, Processor ignores nested data breakpoints
> +	 *    EAX      2      LAS, LFENCE always serializing
> +	 *    EAX      6      NSCB, Null selector clear base
> +	 *    EAX      8      Automatic IBRS
> +	 *
> +	 * Other defined bits are for MSRs that KVM does not expose:
> +	 *   EAX      3      SPCL, SMM page configuration lock
> +	 *   EAX      13     PCMSR, Prefetch control MSR
> +	 */
> +	kvm_cpu_cap_init_scattered(CPUID_8000_0021_EAX,
> +				   SF(NO_NESTED_DATA_BP) | SF(LFENCE_RDTSC) |
> +				   SF(NULL_SEL_CLR_BASE) | SF(AUTOIBRS));
> +	if (static_cpu_has(X86_FEATURE_LFENCE_RDTSC))

Also:

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 61cd33a848cc..acda3883a905 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -744,7 +744,7 @@ void kvm_set_cpu_caps(void)
        kvm_cpu_cap_init_scattered(CPUID_8000_0021_EAX,
                                   SF(NO_NESTED_DATA_BP) | SF(LFENCE_RDTSC) |
                                   SF(NULL_SEL_CLR_BASE) | SF(AUTOIBRS));
-       if (static_cpu_has(X86_FEATURE_LFENCE_RDTSC))
+       if (cpu_feature_enabled(X86_FEATURE_LFENCE_RDTSC))

-- 
Regards/Gruss,
    Boris.

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