linux-kernel - Re: [PATCH] KVM: x86: Expose CLDEMOTE CPU feature to guest VM

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Date:   Mon, 7 May 2018 18:30:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jingqi Liu <jingqi.liu@...el.com>, kvm@...r.kernel.org
Cc:     rkrcmar@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org,
        Wei Wang <wei.w.wang@...el.com>
Subject: Re: [PATCH] KVM: x86: Expose CLDEMOTE CPU feature to guest VM

On 04/05/2018 05:55, Jingqi Liu wrote:
> The CLDEMOTE instruction hints to hardware that the cache line that
> contains the linear address should be moved("demoted") from
> the cache(s) closest to the processor core to a level more distant
> from the processor core. This may accelerate subsequent accesses
> to the line by other cores in the same coherence domain,
> especially if the line was written by the core that demotes the line.
> 
> This patch exposes the cldemote feature to the guest.
> 
> The release document ref below link:
> https://software.intel.com/sites/default/files/managed/c5/15/\
> architecture-instruction-set-extensions-programming-reference.pdf
> This patch has a dependency on https://lkml.org/lkml/2018/4/23/928
> 
> Signed-off-by: Jingqi Liu <jingqi.liu@...el.com>
> Signed-off-by: Wei Wang <wei.w.wang@...el.com>

Thanks.  Note that the Signed-off-by chain for the patch looks strange,
the submitter should be the last (because it is a chain).

In the meanwhile, Ingo, Thomas, would it be possible to get a topic
branch for that patch ("[PATCH] x86/cpufeatures: Enumerate cldemote
instruction")?

Thanks,

Paolo


> ---
>  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 82055b9..72d8c49 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -403,7 +403,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  	const u32 kvm_cpuid_7_0_ecx_x86_features =
>  		F(AVX512VBMI) | F(LA57) | F(PKU) | 0 /*OSPKE*/ |
>  		F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) |
> -		F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG);
> +		F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) |
> +		F(CLDEMOTE);
>  
>  	/* cpuid 7.0.edx*/
>  	const u32 kvm_cpuid_7_0_edx_x86_features =
>