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

Borislav Petkov
2017-07-25T10:26:57Z

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:

---
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)

--
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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