x86/sev: 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 uses a consistent and/or specific GPA for the GHCB associated
with a vCPU. For more information, see the GHCB specification section
"GHCB GPA Registration".

  [ bp: Cleanup comments. ]

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-18-brijesh.singh@amd.com

1 files changed, 34 insertions, 12 deletions

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index cb20fb0c608e..39c87469ee0b 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -41,7 +41,7 @@ static struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);
  * Needs to be in the .data section because we need it NULL before bss is
  * cleared
  */
-static struct ghcb __initdata *boot_ghcb;
+static struct ghcb *boot_ghcb __section(".data");
 
 /* Bitmap of SEV features supported by the hypervisor */
 static u64 sev_hv_features __ro_after_init;
@@ -647,15 +647,39 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 	return ret;
 }
 
-/*
- * This function runs on the first #VC exception after the kernel
- * switched to virtual addresses.
- */
-static bool __init sev_es_setup_ghcb(void)
+static void snp_register_per_cpu_ghcb(void)
 {
+	struct sev_es_runtime_data *data;
+	struct ghcb *ghcb;
+
+	data = this_cpu_read(runtime_data);
+	ghcb = &data->ghcb_page;
+
+	snp_register_ghcb_early(__pa(ghcb));
+}
+
+void setup_ghcb(void)
+{
+	if (!cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
+		return;
+
 	/* First make sure the hypervisor talks a supported protocol. */
 	if (!sev_es_negotiate_protocol())
-		return false;
+		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
+
+	/*
+	 * Check whether the runtime #VC exception handler is active. It uses
+	 * the per-CPU GHCB page which is set up by sev_es_init_vc_handling().
+	 *
+	 * If SNP is active, register the per-CPU GHCB page so that the runtime
+	 * exception handler can use it.
+	 */
+	if (initial_vc_handler == (unsigned long)kernel_exc_vmm_communication) {
+		if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+			snp_register_per_cpu_ghcb();
+
+		return;
+	}
 
 	/*
 	 * Clear the boot_ghcb. The first exception comes in before the bss
@@ -666,7 +690,9 @@ static bool __init sev_es_setup_ghcb(void)
 	/* Alright - Make the boot-ghcb public */
 	boot_ghcb = &boot_ghcb_page;
 
-	return true;
+	/* SNP guest requires that GHCB GPA must be registered. */
+	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		snp_register_ghcb_early(__pa(&boot_ghcb_page));
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -1397,10 +1423,6 @@ bool __init handle_vc_boot_ghcb(struct pt_regs *regs)
 	struct es_em_ctxt ctxt;
 	enum es_result result;
 
-	/* Do initial setup or terminate the guest */
-	if (unlikely(boot_ghcb == NULL && !sev_es_setup_ghcb()))
-		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
-
 	vc_ghcb_invalidate(boot_ghcb);
 
 	result = vc_init_em_ctxt(&ctxt, regs, exit_code);