[PATCH Part1 RFC v3 05/22] x86/sev: Add support for hypervisor feature VMGEXIT

[Brijesh Singh <brijesh.singh@xxxxxxx>]

Version 2 of GHCB specification introduced advertisement of a features
that are supported by the hypervisor. Define the GHCB MSR protocol and NAE
for the hypervisor feature request and query the feature during the GHCB
protocol negotitation. See the GHCB specification for more details.

Version 2 of GHCB specification adds several new NAEs, most of them are
optional except the hypervisor feature. Now that hypervisor feature NAE
is implemented, so bump the GHCB maximum support protocol version.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/include/asm/sev-common.h |  9 +++++++++
 arch/x86/include/asm/sev.h        |  2 +-
 arch/x86/kernel/sev-shared.c      | 21 +++++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index f1e2aacb0d61..981fff2257b9 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -45,6 +45,15 @@
 		(((unsigned long)reg & GHCB_MSR_CPUID_REG_MASK) << GHCB_MSR_CPUID_REG_POS) | \
 		(((unsigned long)fn) << GHCB_MSR_CPUID_FUNC_POS))
 
+/* GHCB Hypervisor Feature Request */
+#define GHCB_MSR_HV_FT_REQ	0x080
+#define GHCB_MSR_HV_FT_RESP	0x081
+#define GHCB_MSR_HV_FT_POS	12
+#define GHCB_MSR_HV_FT_MASK	GENMASK_ULL(51, 0)
+
+#define GHCB_MSR_HV_FT_RESP_VAL(v)	\
+	(((unsigned long)((v) & GHCB_MSR_HV_FT_MASK) >> GHCB_MSR_HV_FT_POS))
+
 #define GHCB_MSR_TERM_REQ		0x100
 #define GHCB_MSR_TERM_REASON_SET_POS	12
 #define GHCB_MSR_TERM_REASON_SET_MASK	0xf
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 7ec91b1359df..134a7c9d91b6 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -13,7 +13,7 @@
 #include <asm/sev-common.h>
 
 #define GHCB_PROTOCOL_MIN	1ULL
-#define GHCB_PROTOCOL_MAX	1ULL
+#define GHCB_PROTOCOL_MAX	2ULL
 #define GHCB_DEFAULT_USAGE	0ULL
 
 #define	VMGEXIT()			{ asm volatile("rep; vmmcall\n\r"); }
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 70f181f20d92..94957c5bdb51 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -20,6 +20,7 @@
  * out when the .bss section is later cleared.
  */
 static u16 ghcb_version __section(".data");
+static u64 hv_features __section(".data");
 
 static bool __init sev_es_check_cpu_features(void)
 {
@@ -49,6 +50,22 @@ static void __noreturn sev_es_terminate(unsigned int set, unsigned int reason)
 		asm volatile("hlt\n" : : : "memory");
 }
 
+static bool get_hv_features(void)
+{
+	u64 val;
+
+	sev_es_wr_ghcb_msr(GHCB_MSR_HV_FT_REQ);
+	VMGEXIT();
+
+	val = sev_es_rd_ghcb_msr();
+	if (GHCB_RESP_CODE(val) != GHCB_MSR_HV_FT_RESP)
+		return false;
+
+	hv_features = GHCB_MSR_HV_FT_RESP_VAL(val);
+
+	return true;
+}
+
 static bool sev_es_negotiate_protocol(void)
 {
 	u64 val;
@@ -67,6 +84,10 @@ static bool sev_es_negotiate_protocol(void)
 
 	ghcb_version = min_t(size_t, GHCB_MSR_PROTO_MAX(val), GHCB_PROTOCOL_MAX);
 
+	/* The hypervisor features are available from version 2 onward. */
+	if ((ghcb_version >= 2) && !get_hv_features())
+		return false;
+
 	return true;
 }
 
-- 
2.17.1