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

Tom Lendacky
2017-07-25T14:29:40Z

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-5C7GfCeVMHo@public.gmane.org>
>>
>> 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-5C7GfCeVMHo@public.gmane.org>
>> Signed-off-by: Brijesh Singh <brijesh.singh-5C7GfCeVMHo@public.gmane.org>
>> ---
>> 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)
>