[RFC PATCH v3 04/20] x86: Handle reduction in physical address size with SME

[Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>]

When System Memory Encryption (SME) is enabled, the physical address
space is reduced. Adjust the x86_phys_bits value to reflect this
reduction.

Signed-off-by: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
---
 arch/x86/include/asm/msr-index.h |    2 ++
 arch/x86/kernel/cpu/common.c     |   30 ++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 56f4c66..4949259 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -336,6 +336,8 @@
 #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/common.c b/arch/x86/kernel/cpu/common.c
index 9bd910a..82c64a6 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -604,6 +604,35 @@ out:
 #endif
 }
 
+/*
+ * AMD Secure Memory Encryption (SME) can reduce the size of the physical
+ * address space if it is enabled, even if memory encryption is not active.
+ * Adjust x86_phys_bits if SME is enabled.
+ */
+static void phys_bits_adjust(struct cpuinfo_x86 *c)
+{
+	u32 eax, ebx, ecx, edx;
+	u64 msr;
+
+	if (c->x86_vendor != X86_VENDOR_AMD)
+		return;
+
+	if (c->extended_cpuid_level < 0x8000001f)
+		return;
+
+	/* Check for SME feature */
+	cpuid(0x8000001f, &eax, &ebx, &ecx, &edx);
+	if (!(eax & 0x01))
+		return;
+
+	/* Check if SME is enabled */
+	rdmsrl(MSR_K8_SYSCFG, msr);
+	if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
+		return;
+
+	c->x86_phys_bits -= (ebx >> 6) & 0x3f;
+}
+
 static void get_cpu_vendor(struct cpuinfo_x86 *c)
 {
 	char *v = c->x86_vendor_id;
@@ -736,6 +765,7 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
 
 		c->x86_virt_bits = (eax >> 8) & 0xff;
 		c->x86_phys_bits = eax & 0xff;
+		phys_bits_adjust(c);
 		c->x86_capability[CPUID_8000_0008_EBX] = ebx;
 	}
 #ifdef CONFIG_X86_32