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

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Date:   Mon, 8 Jan 2018 12:15:41 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Liran Alon <LIRAN.ALON@...cle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>, aliguori@...zon.com,
        Tom Lendacky <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

Reviewed-by: Jim Mattson <jmattson@...gle.com>

On Mon, Jan 8, 2018 at 12:07 PM, Liran Alon <LIRAN.ALON@...cle.com> wrote:
>
>
> 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>