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

[Brian Gerst <brgerst@xxxxxxxxx>]

On Fri, Jul 7, 2017 at 9:38 AM, Tom Lendacky <thomas.lendacky@xxxxxxx> 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@xxxxxxx>
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  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.

>  #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.

>  }
>
>  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.

>         { 0, 0, 0, 0, 0 }
>  };

--
Brian Gerst

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