linux-kernel - Re: [PATCH v2 4/4] x86: vmx: Allow direct access to MSR_IA32_ARCH

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Message-ID: <32627024-026c-4415-8153-bfb9778877b8@redhat.com>
Date:   Mon, 29 Jan 2018 11:45:22 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Asit Mallick <asit.k.mallick@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v2 4/4] x86: vmx: Allow direct access to
 MSR_IA32_ARCH_CAPABILITIES

On 29/01/2018 01:58, KarimAllah Ahmed wrote:
> Add direct access to MSR_IA32_SPEC_CTRL for guests. Future intel processors
> will use this MSR to indicate RDCL_NO (bit 0) and IBRS_ALL (bit 1).

This has to be customizable per-VM (similar to the patches Amazon posted
a while ago for UCODE_REV for example).  It's not urgent anyway given
that no processor has it yet.

Thanks,

Paolo

> Cc: Asit Mallick <asit.k.mallick@...el.com>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Arjan Van De Ven <arjan.van.de.ven@...el.com>
> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Jun Nakajima <jun.nakajima@...el.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Greg KH <gregkh@...uxfoundation.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Ashok Raj <ashok.raj@...el.com>
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
>  arch/x86/kvm/cpuid.c | 4 +++-
>  arch/x86/kvm/vmx.c   | 2 ++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 32c0c14..2339b1a 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -71,6 +71,7 @@ u64 kvm_supported_xcr0(void)
>  #define KVM_CPUID_BIT_AVX512_4VNNIW     2
>  #define KVM_CPUID_BIT_AVX512_4FMAPS     3
>  #define KVM_CPUID_BIT_IBRS              26
> +#define KVM_CPUID_BIT_ARCH_CAPABILITIES 29
>  #define KF(x) bit(KVM_CPUID_BIT_##x)
>  
>  int kvm_update_cpuid(struct kvm_vcpu *vcpu)
> @@ -394,7 +395,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  	/* cpuid 7.0.edx*/
>  	const u32 kvm_cpuid_7_0_edx_x86_features =
>  		KF(AVX512_4VNNIW) | KF(AVX512_4FMAPS) | \
> -		(boot_cpu_has(X86_FEATURE_IBRS) ? KF(IBRS) : 0);
> +		(boot_cpu_has(X86_FEATURE_IBRS) ? KF(IBRS) : 0) | \
> +		(boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES) ? KF(ARCH_CAPABILITIES) : 0);
>  
>  	/* all calls to cpuid_count() should be made on the same cpu */
>  	get_cpu();
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index f82a44c..99cb761 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -9617,6 +9617,8 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>  
>  	if (boot_cpu_has(X86_FEATURE_IBPB))
>  		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PRED_CMD, MSR_TYPE_RW);
> +	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_ARCH_CAPABILITIES, MSR_TYPE_R);
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_FS_BASE, MSR_TYPE_RW);
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_GS_BASE, MSR_TYPE_RW);
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_KERNEL_GS_BASE, MSR_TYPE_RW);
>