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Subject: [PATCH Part1 RFC v2 12/20] x86/compressed: Register GHCB memory when SEV-SNP is active
Date:   Fri, 30 Apr 2021 07:16:08 -0500
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The SEV-SNP guest is required to perform GHCB GPA registration. This is
because the hypervisor may prefer that a guest use a consistent and/or
specific GPA for the GHCB associated with a vCPU. For more information,
see the GHCB specification.

If hypervisor can not work with the guest provided GPA then terminate the
guest boot.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 arch/x86/boot/compressed/sev.c    |  4 ++++
 arch/x86/include/asm/sev-common.h | 12 ++++++++++++
 arch/x86/kernel/sev-shared.c      | 16 ++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 4f215d0c9f76..07b9529d7d95 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -206,6 +206,10 @@ static bool early_setup_sev_es(void)
 	/* Initialize lookup tables for the instruction decoder */
 	inat_init_tables();
 
+	/* SEV-SNP guest requires the GHCB GPA must be registered */
+	if (sev_snp_enabled())
+		snp_register_ghcb(__pa(&boot_ghcb_page));
+
 	return true;
 }
 
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 733fca403ae5..7487d4768ef0 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -88,6 +88,18 @@
 #define GHCB_MSR_PSC_RSVD_MASK		0xfffffULL
 #define GHCB_MSR_PSC_RESP_VAL(val)	((val) >> GHCB_MSR_PSC_ERROR_POS)
 
+/* GHCB GPA Register */
+#define GHCB_MSR_GPA_REG_REQ		0x012
+#define GHCB_MSR_GPA_REG_VALUE_POS	12
+#define GHCB_MSR_GPA_REG_VALUE_MASK	0xfffffffffffffULL
+#define GHCB_MSR_GPA_REQ_VAL(v)		\
+		(((v) << GHCB_MSR_GPA_REG_VALUE_POS) | GHCB_MSR_GPA_REG_REQ)
+
+#define GHCB_MSR_GPA_REG_RESP		0x013
+#define GHCB_MSR_GPA_REG_RESP_VAL(v)	((v) >> GHCB_MSR_GPA_REG_VALUE_POS)
+#define GHCB_MSR_GPA_REG_ERROR		0xfffffffffffffULL
+#define GHCB_MSR_GPA_INVALID		~0ULL
+
 /* SNP Page State Change NAE event */
 #define VMGEXIT_PSC_MAX_ENTRY		253
 #define VMGEXIT_PSC_INVALID_HEADER	0x100000001
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 085d3d724bc8..140c5bc07fc2 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -81,6 +81,22 @@ static bool ghcb_get_hv_features(void)
 	return true;
 }
 
+static void snp_register_ghcb(unsigned long paddr)
+{
+	unsigned long pfn = paddr >> PAGE_SHIFT;
+	u64 val;
+
+	sev_es_wr_ghcb_msr(GHCB_MSR_GPA_REQ_VAL(pfn));
+	VMGEXIT();
+
+	val = sev_es_rd_ghcb_msr();
+
+	/* If the response GPA is not ours then abort the guest */
+	if ((GHCB_RESP_CODE(val) != GHCB_MSR_GPA_REG_RESP) ||
+	    (GHCB_MSR_GPA_REG_RESP_VAL(val) != pfn))
+		sev_es_terminate(1, GHCB_TERM_REGISTER);
+}
+
 static bool sev_es_negotiate_protocol(void)
 {
 	u64 val;
-- 
2.17.1