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

--
Brian Gerst

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