x86/compressed: Register GHCB memory when SEV-SNP is active

The SEV-SNP guest is required by the GHCB spec to register the GHCB's Guest Physical Address (GPA). 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 section "GHCB GPA Registration". If hypervisor can not work with the guest provided GPA then terminate the guest boot. Signed-off-by: Brijesh Singh <[email protected]> Signed-off-by: Borislav Petkov <[email protected]> Reviewed-by: Venu Busireddy <[email protected]> Link: https://lore.kernel.org/r/[email protected]
ambv · Apr 6, 2022 · 87294bd · 87294bd
1 parent 4f9c403
commit 87294bd
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diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
@@ -175,6 +175,10 @@ static bool early_setup_ghcb(void)
 	/* Initialize lookup tables for the instruction decoder */
 	inat_init_tables();
 
+	/* SNP guest requires the GHCB GPA must be registered */
+	if (sev_snp_enabled())
+		snp_register_ghcb_early(__pa(&boot_ghcb_page));
+
 	return true;
 }
 

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
@@ -57,6 +57,19 @@
 #define GHCB_MSR_AP_RESET_HOLD_REQ	0x006
 #define GHCB_MSR_AP_RESET_HOLD_RESP	0x007
 
+/* GHCB GPA Register */
+#define GHCB_MSR_REG_GPA_REQ		0x012
+#define GHCB_MSR_REG_GPA_REQ_VAL(v)			\
+	/* GHCBData[63:12] */				\
+	(((u64)((v) & GENMASK_ULL(51, 0)) << 12) |	\
+	/* GHCBData[11:0] */				\
+	GHCB_MSR_REG_GPA_REQ)
+
+#define GHCB_MSR_REG_GPA_RESP		0x013
+#define GHCB_MSR_REG_GPA_RESP_VAL(v)			\
+	/* GHCBData[63:12] */				\
+	(((u64)(v) & GENMASK_ULL(63, 12)) >> 12)
+
 /*
  * SNP Page State Change Operation
  *

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
@@ -68,6 +68,22 @@ static u64 get_hv_features(void)
 	return GHCB_MSR_HV_FT_RESP_VAL(val);
 }
 
+static void __maybe_unused snp_register_ghcb_early(unsigned long paddr)
+{
+	unsigned long pfn = paddr >> PAGE_SHIFT;
+	u64 val;
+
+	sev_es_wr_ghcb_msr(GHCB_MSR_REG_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_REG_GPA_RESP) ||
+	    (GHCB_MSR_REG_GPA_RESP_VAL(val) != pfn))
+		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_REGISTER);
+}
+
 static bool sev_es_negotiate_protocol(void)
 {
 	u64 val;