Re: [PATCH v9 04/38] x86/CPU/AMD: Add the Secure Memory Encryption CPU feature

[Tom Lendacky <thomas.lendacky@amd.com>]

On 7/11/2017 12:07 AM, Brian Gerst wrote:
> On Mon, Jul 10, 2017 at 3:41 PM, Tom Lendacky <thomas.lendacky@amd.com> wrote:
>> On 7/8/2017 7:50 AM, Brian Gerst wrote:
>>>
>>> On Fri, Jul 7, 2017 at 9:38 AM, Tom Lendacky <thomas.lendacky@amd.com>
>>> wrote:
>>>>
>>>> Update the CPU features to include identifying and reporting on the
>>>> Secure Memory Encryption (SME) feature.  SME is identified by CPUID
>>>> 0x8000001f, but requires BIOS support to enable it (set bit 23 of
>>>> MSR_K8_SYSCFG).  Only show the SME feature as available if reported by
>>>> CPUID and enabled by BIOS.
>>>>
>>>> Reviewed-by: Borislav Petkov <bp@suse.de>
>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>>> ---
>>>>    arch/x86/include/asm/cpufeatures.h |    1 +
>>>>    arch/x86/include/asm/msr-index.h   |    2 ++
>>>>    arch/x86/kernel/cpu/amd.c          |   13 +++++++++++++
>>>>    arch/x86/kernel/cpu/scattered.c    |    1 +
>>>>    4 files changed, 17 insertions(+)
>>>>
>>>> diff --git a/arch/x86/include/asm/cpufeatures.h
>>>> b/arch/x86/include/asm/cpufeatures.h
>>>> index 2701e5f..2b692df 100644
>>>> --- a/arch/x86/include/asm/cpufeatures.h
>>>> +++ b/arch/x86/include/asm/cpufeatures.h
>>>> @@ -196,6 +196,7 @@
>>>>
>>>>    #define X86_FEATURE_HW_PSTATE  ( 7*32+ 8) /* AMD HW-PState */
>>>>    #define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD
>>>> ProcFeedbackInterface */
>>>> +#define X86_FEATURE_SME                ( 7*32+10) /* AMD Secure Memory
>>>> Encryption */
>>>
>>>
>>> Given that this feature is available only in long mode, this should be
>>> added to disabled-features.h as disabled for 32-bit builds.
>>
>>
>> I can add that.  If the series needs a re-spin then I'll include this
>> change in the series, otherwise I can send a follow-on patch to handle
>> the feature for 32-bit builds if that works.
>>
>>
>>>
>>>>    #define X86_FEATURE_INTEL_PPIN ( 7*32+14) /* Intel Processor Inventory
>>>> Number */
>>>>    #define X86_FEATURE_INTEL_PT   ( 7*32+15) /* Intel Processor Trace */
>>>> diff --git a/arch/x86/include/asm/msr-index.h
>>>> b/arch/x86/include/asm/msr-index.h
>>>> index 18b1623..460ac01 100644
>>>> --- a/arch/x86/include/asm/msr-index.h
>>>> +++ b/arch/x86/include/asm/msr-index.h
>>>> @@ -352,6 +352,8 @@
>>>>    #define MSR_K8_TOP_MEM1                        0xc001001a
>>>>    #define MSR_K8_TOP_MEM2                        0xc001001d
>>>>    #define MSR_K8_SYSCFG                  0xc0010010
>>>> +#define MSR_K8_SYSCFG_MEM_ENCRYPT_BIT  23
>>>> +#define MSR_K8_SYSCFG_MEM_ENCRYPT
>>>> BIT_ULL(MSR_K8_SYSCFG_MEM_ENCRYPT_BIT)
>>>>    #define MSR_K8_INT_PENDING_MSG         0xc0010055
>>>>    /* C1E active bits in int pending message */
>>>>    #define K8_INTP_C1E_ACTIVE_MASK                0x18000000
>>>> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
>>>> index bb5abe8..c47ceee 100644
>>>> --- a/arch/x86/kernel/cpu/amd.c
>>>> +++ b/arch/x86/kernel/cpu/amd.c
>>>> @@ -611,6 +611,19 @@ static void early_init_amd(struct cpuinfo_x86 *c)
>>>>            */
>>>>           if (cpu_has_amd_erratum(c, amd_erratum_400))
>>>>                   set_cpu_bug(c, X86_BUG_AMD_E400);
>>>> +
>>>> +       /*
>>>> +        * BIOS support is required for SME. If BIOS has not enabled SME
>>>> +        * then don't advertise the feature (set in scattered.c)
>>>> +        */
>>>> +       if (cpu_has(c, X86_FEATURE_SME)) {
>>>> +               u64 msr;
>>>> +
>>>> +               /* Check if SME is enabled */
>>>> +               rdmsrl(MSR_K8_SYSCFG, msr);
>>>> +               if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
>>>> +                       clear_cpu_cap(c, X86_FEATURE_SME);
>>>> +       }
>>>
>>>
>>> This should be conditional on CONFIG_X86_64.
>>
>>
>> If I make the scattered feature support conditional on CONFIG_X86_64
>> (based on comment below) then cpu_has() will always be false unless
>> CONFIG_X86_64 is enabled. So this won't need to be wrapped by the
>> #ifdef.
> 
> If you change it to use cpu_feature_enabled(), gcc will see that it is
> disabled and eliminate the dead code at compile time.
> 
>>>
>>>>    }
>>>>
>>>>    static void init_amd_k8(struct cpuinfo_x86 *c)
>>>> diff --git a/arch/x86/kernel/cpu/scattered.c
>>>> b/arch/x86/kernel/cpu/scattered.c
>>>> index 23c2350..05459ad 100644
>>>> --- a/arch/x86/kernel/cpu/scattered.c
>>>> +++ b/arch/x86/kernel/cpu/scattered.c
>>>> @@ -31,6 +31,7 @@ struct cpuid_bit {
>>>>           { X86_FEATURE_HW_PSTATE,        CPUID_EDX,  7, 0x80000007, 0 },
>>>>           { X86_FEATURE_CPB,              CPUID_EDX,  9, 0x80000007, 0 },
>>>>           { X86_FEATURE_PROC_FEEDBACK,    CPUID_EDX, 11, 0x80000007, 0 },
>>>> +       { X86_FEATURE_SME,              CPUID_EAX,  0, 0x8000001f, 0 },
>>>
>>>
>>> This should also be conditional.  We don't want to set this feature on
>>> 32-bit, even if the processor has support.
>>
>>
>> Can do.  See comment above about re-spin vs. follow-on patch.
>>
>> Thanks,
>> Tom
> 
> A followup patch will be OK if there is no code that will get confused
> by the SME bit being present but not active.

The feature bit is mainly there for /proc/cpuinfo. The code uses
sme_active() in order to determine how to behave. Under CONFIG_X86_32,
sme_active() is always 0.

Based on the comment related to patch 7 (ioremap() of ISA range) I may
need to re-spin the patchset.  I'll include this change following
the recommendation from Boris to use the IS_ENABLED(CONFIG_X86_32) check
to clear the feature bit.

Thanks,
Tom

> 
> --
> Brian Gerst
> 

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