linux-kernel - Re: [PATCH] KVM: VMX: Expose SSBD properly to guests.

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Date:   Thu, 7 Jun 2018 15:14:14 +0200 (CEST)
From:   Thomas Voegtle <tv@...96.de>
To:     Ben Hutchings <ben@...adent.org.uk>
cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, stable@...r.kernel.org
Subject: Re: [PATCH] KVM: VMX: Expose SSBD properly to guests.

On Wed, 23 May 2018, Ben Hutchings wrote:

> On Mon, 2018-05-21 at 17:54 -0400, Konrad Rzeszutek Wilk wrote:
>> The X86_FEATURE_SSBD is an synthetic CPU feature - that is
>> it bit location has no relevance to the real CPUID 0x7.EBX[31]
>> bit position. For that we need the new CPU feature name.
>>
>> Fixes: 52817587e706 ("x86/cpufeatures: Disentangle SSBD enumeration")
>>
>> CC: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: "Radim Krčmář" <rkrcmar@...hat.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>> ---
>>  arch/x86/kvm/cpuid.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index ced851169730..598461e24be3 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -407,8 +407,8 @@ 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 =
>> -		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) | F(SSBD) |
>> -		F(ARCH_CAPABILITIES);
>> +		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |
>> +		F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES);
>>
>>  	/* all calls to cpuid_count() should be made on the same cpu */
>>  	get_cpu();
>
> For 4.9-stable, guest_cpuid_has_spec_ctrl() needs a similar fix.
>
> Ben.

Do you mean something like this?

--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -179,7 +179,7 @@ static inline bool guest_cpuid_has_spec_ctrl(struct 
kvm_vcpu *vcpu)
         if (best && (best->ebx & bit(X86_FEATURE_AMD_IBRS)))
                 return true;
         best = kvm_find_cpuid_entry(vcpu, 7, 0);
-       return best && (best->edx & (bit(X86_FEATURE_SPEC_CTRL) | 
bit(X86_FEATURE_SSBD)));
+       return best && (best->edx & (bit(X86_FEATURE_SPEC_CTRL) | 
bit(X86_FEATURE_SPEC_CTRL_SSBD)));
  }

  static inline bool guest_cpuid_has_arch_capabilities(struct kvm_vcpu 
*vcpu)