linux-kernel - Re: [PATCH 7/7] KVM: x86: add SPEC_CTRL and IBPB

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Date:   Mon, 08 Jan 2018 22:07:26 +0200
From:   Liran Alon <LIRAN.ALON@...CLE.COM>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
CC:     jmattson@...gle.com, aliguori@...zon.com, thomas.lendacky@....com,
        dwmw@...zon.co.uk, bp@...en8.de
Subject: Re: [PATCH 7/7] KVM: x86: add SPEC_CTRL and IBPB_SUPPORT to MSR and
 CPUID lists



On 08/01/18 20:08, Paolo Bonzini wrote:
> Expose them to userspace, now that guests can use them.
> I am not adding cpufeatures here to avoid having a kernel
> that shows spec_ctrl in /proc/cpuinfo and actually has no
> support whatsoever for IBRS/IBPB.  Keep the ugly special-casing
> for now, and clean it up once the generic arch/x86/ code
> learns about them.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>   arch/x86/kvm/cpuid.c | 24 +++++++++++++++++++++---
>   arch/x86/kvm/x86.c   |  1 +
>   2 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 767af697c20c..5f43a5940275 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -397,7 +397,12 @@ 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);
> +		KF(AVX512_4VNNIW) | KF(AVX512_4FMAPS) |
> +		KF(SPEC_CTRL) | KF(STIBP);
> +
> +	/* cpuid 0x80000008.edx */
> +	const u32 kvm_cpuid_80000008_ebx_x86_features =
> +		KF(IBPB_SUPPORT);
>
>   	/* all calls to cpuid_count() should be made on the same cpu */
>   	get_cpu();
> @@ -483,7 +488,14 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>   			if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE))
>   				entry->ecx &= ~F(PKU);
>   			entry->edx &= kvm_cpuid_7_0_edx_x86_features;
> -			entry->edx &= get_scattered_cpuid_leaf(7, 0, CPUID_EDX);
> +			/*
> +			 * FIXME: the special casing of SPEC_CTRL and STIBP
> +			 * can be removed once they become regular
> +			 * cpufeatures.
> +			 */
> +			entry->edx &= (
> +				get_scattered_cpuid_leaf(7, 0, CPUID_EDX) |
> +				KF(SPEC_CTRL) | KF(STIBP));
>   		} else {
>   			entry->ebx = 0;
>   			entry->ecx = 0;
> @@ -651,7 +663,13 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>   		if (!g_phys_as)
>   			g_phys_as = phys_as;
>   		entry->eax = g_phys_as | (virt_as << 8);
> -		entry->ebx = entry->edx = 0;
> +		/*
> +		 * FIXME: mask against cpufeatures, with
> +		 * get_scattered_cpuid_leaf(0x80000008, 0, CPUID_EBX),
> +		 * once IBPB_SUPPORT becomes a regular cpufeature.
> +		 */
> +		entry->ebx &= kvm_cpuid_80000008_ebx_x86_features;
> +		entry->edx = 0;
>   		break;
>   	}
>   	case 0x80000019:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index daa1918031df..4abb37d9f4d8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1032,6 +1032,7 @@ unsigned int kvm_get_pt_addr_cnt(void)
>   	MSR_IA32_RTIT_ADDR1_A, MSR_IA32_RTIT_ADDR1_B,
>   	MSR_IA32_RTIT_ADDR2_A, MSR_IA32_RTIT_ADDR2_B,
>   	MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
> +	MSR_IA32_SPEC_CTRL,
>   };
>
>   static unsigned num_msrs_to_save;
>

Reviewed-by: Liran Alon <liran.alon@...cle.com>