[Patch v3 3/4] x86/sev: Add guest support for Enhanced SMT Protection

[Pratik R. Sampat]

Enhanced SMT Protection requires every VMSA to carry the vCPU's identity
and the mask of SMT siblings it may co-run with. The guest builds the
VMSA itself when bringing up an AP, so populate both fields there, before
the page is turned into a VMSA and while it is still writable.

Fully set the sibling mask so that all threads of the same guest trust
each other.

Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Pratik R. Sampat <prsampat@xxxxxxx>
---
v2..v3:
* Collected Reviewed-by from Tom
* Use sev_status to determine SNP support for guest as well - Tom

v1..v2:
* Add ESMTP to SNP_FEATURES_IMPL and SNP_FEATURES_IMPL_REQ  
---
 arch/x86/boot/compressed/sev.c   |  6 ++++--
 arch/x86/coco/sev/core.c         | 13 +++++++++++++
 arch/x86/include/asm/msr-index.h |  4 +++-
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index c6512f2ea31e..4e0fa5a5f70b 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -188,7 +188,8 @@ bool sev_es_check_ghcb_fault(unsigned long address)
 				 MSR_AMD64_SNP_RESERVED_BIT13 |		\
 				 MSR_AMD64_SNP_RESERVED_BIT15 |		\
 				 MSR_AMD64_SNP_SECURE_AVIC |		\
-				 MSR_AMD64_SNP_RESERVED_BITS19_22 |	\
+				 MSR_AMD64_SNP_ESMT_PROT |		\
+				 MSR_AMD64_SNP_RESERVED_BITS20_22 |	\
 				 MSR_AMD64_SNP_RESERVED_MASK)
 
 #ifdef CONFIG_AMD_SECURE_AVIC
@@ -204,7 +205,8 @@ bool sev_es_check_ghcb_fault(unsigned long address)
  */
 #define SNP_FEATURES_IMPL	(MSR_AMD64_SNP_DEBUG_SWAP |	\
 				 MSR_AMD64_SNP_SECURE_TSC |	\
-				 SNP_FEATURE_SECURE_AVIC)
+				 SNP_FEATURE_SECURE_AVIC |	\
+				 MSR_AMD64_SNP_ESMT_PROT)
 
 u64 snp_get_unsupported_features(u64 status)
 {
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index cc292d7c6fd1..b89766bb9365 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -89,6 +89,7 @@ static const char * const sev_status_feat_names[] = {
 	[MSR_AMD64_SNP_VMSA_REG_PROT_BIT]	= "VMSARegProt",
 	[MSR_AMD64_SNP_SMT_PROT_BIT]		= "SMTProt",
 	[MSR_AMD64_SNP_SECURE_AVIC_BIT]		= "SecureAVIC",
+	[MSR_AMD64_SNP_ESMT_PROT_BIT]		= "ESMTProt",
 	[MSR_AMD64_SNP_IBPB_ON_ENTRY_BIT]	= "IBPBOnEntry",
 };
 
@@ -849,6 +850,18 @@ static int wakeup_cpu_via_vmgexit(u32 apic_id, unsigned long start_ip, unsigned
 	vmsa->vmpl		= snp_vmpl;
 	vmsa->sev_features	= sev_status >> 2;
 
+	if (sev_status & MSR_AMD64_SEV_SNP_ENABLED &&
+	    (sev_status & MSR_AMD64_SNP_ESMT_PROT)) {
+		vmsa->vcpu_id = apic_id;
+		/*
+		 * The mask fully set puts every vCPU in one group, so any two
+		 * of them may be co-resident. A legal ESMTP sibling must
+		 * also match on ASID, so the sibling of a vCPU in guest mode is
+		 * always either another vCPU of this same guest or idle.
+		 */
+		vmsa->vcpu_sibling_mask = U32_MAX;
+	}
+
 	/* Populate AP's TSC scale/offset to get accurate TSC values. */
 	if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC)) {
 		vmsa->tsc_scale = snp_tsc_scale;
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index fbcb3313e946..6fd26151d146 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -745,7 +745,9 @@
 #define MSR_AMD64_SNP_SMT_PROT		BIT_ULL(MSR_AMD64_SNP_SMT_PROT_BIT)
 #define MSR_AMD64_SNP_SECURE_AVIC_BIT	18
 #define MSR_AMD64_SNP_SECURE_AVIC	BIT_ULL(MSR_AMD64_SNP_SECURE_AVIC_BIT)
-#define MSR_AMD64_SNP_RESERVED_BITS19_22 GENMASK_ULL(22, 19)
+#define MSR_AMD64_SNP_ESMT_PROT_BIT	19
+#define MSR_AMD64_SNP_ESMT_PROT	BIT_ULL(MSR_AMD64_SNP_ESMT_PROT_BIT)
+#define MSR_AMD64_SNP_RESERVED_BITS20_22 GENMASK_ULL(22, 20)
 #define MSR_AMD64_SNP_IBPB_ON_ENTRY_BIT	23
 #define MSR_AMD64_SNP_IBPB_ON_ENTRY	BIT_ULL(MSR_AMD64_SNP_IBPB_ON_ENTRY_BIT)
 #define MSR_AMD64_SNP_RESV_BIT		24
-- 
2.43.0