Re: [RFC Part1 PATCH v3 02/17] x86/CPU/AMD: Add the Secure Encrypted Virtualization CPU feature

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

On 7/25/2017 5:26 AM, Borislav Petkov wrote:
> On Mon, Jul 24, 2017 at 02:07:42PM -0500, Brijesh Singh wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> Update the CPU features to include identifying and reporting on the
>> Secure Encrypted Virtualization (SEV) feature.  SME is identified by
>> CPUID 0x8000001f, but requires BIOS support to enable it (set bit 23 of
>> MSR_K8_SYSCFG and set bit 0 of MSR_K7_HWCR).  Only show the SEV feature
>> as available if reported by CPUID and enabled by BIOS.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> ---
>>   arch/x86/include/asm/cpufeatures.h |  1 +
>>   arch/x86/include/asm/msr-index.h   |  2 ++
>>   arch/x86/kernel/cpu/amd.c          | 30 +++++++++++++++++++++++++-----
>>   arch/x86/kernel/cpu/scattered.c    |  1 +
>>   4 files changed, 29 insertions(+), 5 deletions(-)
> 
> ...
> 
>> @@ -637,6 +642,21 @@ static void early_init_amd(struct cpuinfo_x86 *c)
>>   			clear_cpu_cap(c, X86_FEATURE_SME);
>>   		}
>>   	}
>> +
>> +	if (cpu_has(c, X86_FEATURE_SEV)) {
>> +		if (IS_ENABLED(CONFIG_X86_32)) {
>> +			clear_cpu_cap(c, X86_FEATURE_SEV);
>> +		} else {
>> +			u64 syscfg, hwcr;
>> +
>> +			/* Check if SEV is enabled */
>> +			rdmsrl(MSR_K8_SYSCFG, syscfg);
>> +			rdmsrl(MSR_K7_HWCR, hwcr);
>> +			if (!(syscfg & MSR_K8_SYSCFG_MEM_ENCRYPT) ||
>> +			    !(hwcr & MSR_K7_HWCR_SMMLOCK))
>> +				clear_cpu_cap(c, X86_FEATURE_SEV);
>> +		}
>> +	}
> 
> Let's simplify this and read the MSRs only once. Diff ontop. Please
> check if I'm missing a case:

Yup, we can do something like that.  I believe the only change that
would be needed to your patch would be to move the IS_ENABLED() check
to after the physical address space reduction check.

Thanks,
Tom

> 
> ---
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index c413f04bdd41..79af07731ab1 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -546,6 +546,48 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
>   	}
>   }
>   
> +static void early_detect_mem_enc(struct cpuinfo_x86 *c)
> +{
> +	u64 syscfg, hwcr;
> +
> +	/*
> +	 * BIOS support is required for SME and SEV.
> +	 *   For SME: If BIOS has enabled SME then adjust x86_phys_bits by
> +	 *	      the SME physical address space reduction value.
> +	 *	      If BIOS has not enabled SME then don't advertise the
> +	 *	      SME feature (set in scattered.c).
> +	 *   For SEV: If BIOS has not enabled SEV then don't advertise the
> +	 *            SEV feature (set in scattered.c).
> +	 *
> +	 *   In all cases, since support for SME and SEV requires long mode,
> +	 *   don't advertise the feature under CONFIG_X86_32.
> +	 */
> +	if (cpu_has(c, X86_FEATURE_SME) ||
> +	    cpu_has(c, X86_FEATURE_SEV)) {
> +
> +		if (IS_ENABLED(CONFIG_X86_32))
> +			goto clear;
> +
> +		/* Check if SME is enabled */
> +		rdmsrl(MSR_K8_SYSCFG, syscfg);
> +		if (!(syscfg & MSR_K8_SYSCFG_MEM_ENCRYPT))
> +			goto clear;
> +
> +		c->x86_phys_bits -= (cpuid_ebx(0x8000001f) >> 6) & 0x3f;
> +
> +		/* Check if SEV is enabled */
> +		rdmsrl(MSR_K7_HWCR, hwcr);
> +		if (!(hwcr & MSR_K7_HWCR_SMMLOCK))
> +			goto clear_sev;
> +
> +		return;
> +clear:
> +		clear_cpu_cap(c, X86_FEATURE_SME);
> +clear_sev:
> +		clear_cpu_cap(c, X86_FEATURE_SEV);
> +	}
> +}
> +
>   static void early_init_amd(struct cpuinfo_x86 *c)
>   {
>   	u32 dummy;
> @@ -617,46 +659,8 @@ 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 and SEV.
> -	 *   For SME: If BIOS has enabled SME then adjust x86_phys_bits by
> -	 *	      the SME physical address space reduction value.
> -	 *	      If BIOS has not enabled SME then don't advertise the
> -	 *	      SME feature (set in scattered.c).
> -	 *   For SEV: If BIOS has not enabled SEV then don't advertise the
> -	 *            SEV feature (set in scattered.c).
> -	 *
> -	 *   In all cases, since support for SME and SEV requires long mode,
> -	 *   don't advertise the feature under CONFIG_X86_32.
> -	 */
> -	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) {
> -			c->x86_phys_bits -= (cpuid_ebx(0x8000001f) >> 6) & 0x3f;
> -			if (IS_ENABLED(CONFIG_X86_32))
> -				clear_cpu_cap(c, X86_FEATURE_SME);
> -		} else {
> -			clear_cpu_cap(c, X86_FEATURE_SME);
> -		}
> -	}
> +	early_detect_mem_enc(c);
>   
> -	if (cpu_has(c, X86_FEATURE_SEV)) {
> -		if (IS_ENABLED(CONFIG_X86_32)) {
> -			clear_cpu_cap(c, X86_FEATURE_SEV);
> -		} else {
> -			u64 syscfg, hwcr;
> -
> -			/* Check if SEV is enabled */
> -			rdmsrl(MSR_K8_SYSCFG, syscfg);
> -			rdmsrl(MSR_K7_HWCR, hwcr);
> -			if (!(syscfg & MSR_K8_SYSCFG_MEM_ENCRYPT) ||
> -			    !(hwcr & MSR_K7_HWCR_SMMLOCK))
> -				clear_cpu_cap(c, X86_FEATURE_SEV);
> -		}
> -	}
>   }
>   
>   static void init_amd_k8(struct cpuinfo_x86 *c)
>