linux-kernel - Re: [PATCH v3 2/2] x86/kvm: Expose new features for supported cpuid

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Date:   Sun, 9 Aug 2020 19:14:13 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Cathy Zhang <cathy.zhang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     sean.j.christopherson@...el.com, gregkh@...uxfoundation.org,
        tglx@...utronix.de, tony.luck@...el.com, dave.hansen@...el.com,
        kyung.min.park@...el.com, ricardo.neri-calderon@...ux.intel.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        jpoimboe@...hat.com, ak@...ux.intel.com, ravi.v.shankar@...el.com
Subject: Re: [PATCH v3 2/2] x86/kvm: Expose new features for supported cpuid

On 09/08/20 09:47, Cathy Zhang wrote:
> Expose the SERIALIZE and TSX Suspend Load Address Tracking
> features in KVM CPUID, so when running on processors which
> support them, KVM could pass this information to guests and
> they can make use of these features accordingly.
> 
> SERIALIZE is a faster serializing instruction which does not modify
> registers, arithmetic flags or memory, will not cause VM exit. It's
> availability is indicated by CPUID.(EAX=7,ECX=0):ECX[bit 14].
> 
> TSX suspend load tracking instruction aims to give a way to choose
> which memory accesses do not need to be tracked in the TSX read set.
> It's availability is indicated as CPUID.(EAX=7,ECX=0):EDX[bit 16].
> 
> Those instructions are currently documented in the the latest "extensions"
> manual (ISE). It will appear in the "main" manual (SDM) in the future.
> 
> Signed-off-by: Cathy Zhang <cathy.zhang@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---
> Changes since v2:
>  * Merge two patches into a single one. (Luck, Tony)
>  * Add overview introduction for features. (Sean Christopherson)
>  * Refactor commit message to explain why expose feature bits. (Luck, Tony)
> ---
>  arch/x86/kvm/cpuid.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8a294f9..dcf48cc 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -341,7 +341,8 @@ void kvm_set_cpu_caps(void)
>  	kvm_cpu_cap_mask(CPUID_7_EDX,
>  		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |
>  		F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) |
> -		F(MD_CLEAR) | F(AVX512_VP2INTERSECT) | F(FSRM)
> +		F(MD_CLEAR) | F(AVX512_VP2INTERSECT) | F(FSRM) |
> +		F(SERIALIZE) | F(TSXLDTRK)
>  	);
>  
>  	/* TSC_ADJUST and ARCH_CAPABILITIES are emulated in software. */
> 

TSXLDTRK is not going to be in 5.9 as far as I can see, so I split back
again the patches (this is why I prefer them to be split, sorry Tony :))
and committed the SERIALIZE part.

Paolo