linux-kernel - Re: [PATCH 1/2] kvm/x86/vmx: enable X86_FEATURE

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Date:   Tue, 26 May 2020 18:20:39 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Tao Xu <tao3.xu@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jingqi Liu <jingqi.liu@...el.com>
Subject: Re: [PATCH 1/2] kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM
 capabilities

On Sat, May 23, 2020 at 07:14:54PM +0300, Maxim Levitsky wrote:
> Even though we might not allow the guest to use
> WAITPKG's new instructions, we should tell KVM
> that the feature is supported by the host CPU.
> 
> Note that vmx_waitpkg_supported checks that WAITPKG
> _can_ be set in secondary execution controls as specified
> by VMX capability MSR, rather that we actually enable it for a guest.

These line wraps are quite weird and inconsistent.

> 
> Fixes: e69e72faa3a0 KVM: x86: Add support for user wait instructions

Checkpatch doesn't complain,  but the preferred Fixes format is

  Fixes: e69e72faa3a07 ("KVM: x86: Add support for user wait instructions")

e.g.

  git show -s --pretty='tformat:%h ("%s")'

For the code itself:

Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>

> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 55712dd86bafa..fca493d4517c5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7298,6 +7298,9 @@ static __init void vmx_set_cpu_caps(void)
>  	/* CPUID 0x80000001 */
>  	if (!cpu_has_vmx_rdtscp())
>  		kvm_cpu_cap_clear(X86_FEATURE_RDTSCP);
> +
> +	if (vmx_waitpkg_supported())
> +		kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
>  }
>  
>  static void vmx_request_immediate_exit(struct kvm_vcpu *vcpu)
> -- 
> 2.26.2
>