x86/sev: Allow non-VMPL0 execution when an SVSM is present

To allow execution at a level other than VMPL0, an SVSM must be present.
Allow the SEV-SNP guest to continue booting if an SVSM is detected and
the hypervisor supports the SVSM feature as indicated in the GHCB
hypervisor features bitmap.

  [ bp: Massage a bit. ]
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/2ce7cf281cce1d0cba88f3f576687ef75dc3c953.1717600736.git.thomas.lendacky@amd.com

arch/x86/boot/compressed/sev.c

@@ -610,11 +610,15 @@ void sev_enable(struct boot_params *bp)
 	 * features.
 	 */
 	if (sev_status & MSR_AMD64_SEV_SNP_ENABLED) {
-		if (!(get_hv_features() & GHCB_HV_FT_SNP))
+		u64 hv_features;
+		int ret;
+
+		hv_features = get_hv_features();
+		if (!(hv_features & GHCB_HV_FT_SNP))
 			sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
 
 		/*
-		 * Enforce running at VMPL0.
+		 * Enforce running at VMPL0 or with an SVSM.
 		 *
 		 * Use RMPADJUST (see the rmpadjust() function for a description of
 		 * what the instruction does) to update the VMPL1 permissions of a
@@ -623,7 +627,14 @@ void sev_enable(struct boot_params *bp)
 		 * only ever run at a single VMPL level so permission mask changes of a
 		 * lesser-privileged VMPL are a don't-care.
 		 */
-		if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1))
+		ret = rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1);
+
+		/*
+		 * Running at VMPL0 is not required if an SVSM is present and the hypervisor
+		 * supports the required SVSM GHCB events.
+		 */
+		if (ret &&
+		    !(snp_vmpl && (hv_features & GHCB_HV_FT_SNP_MULTI_VMPL)))
 			sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
 	}
 

arch/x86/include/asm/sev-common.h

@@ -122,6 +122,7 @@ enum psc_op {
 
 #define GHCB_HV_FT_SNP			BIT_ULL(0)
 #define GHCB_HV_FT_SNP_AP_CREATION	BIT_ULL(1)
+#define GHCB_HV_FT_SNP_MULTI_VMPL	BIT_ULL(5)
 
 /*
  * SNP Page State Change NAE event

arch/x86/kernel/sev.c

@@ -2352,23 +2352,27 @@ static void dump_cpuid_table(void)
  * expected, but that initialization happens too early in boot to print any
  * sort of indicator, and there's not really any other good place to do it,
  * so do it here.
+ *
+ * If running as an SNP guest, report the current VM privilege level (VMPL).
  */
-static int __init report_cpuid_table(void)
+static int __init report_snp_info(void)
 {
 	const struct snp_cpuid_table *cpuid_table = snp_cpuid_get_table();
 
-	if (!cpuid_table->count)
-		return 0;
+	if (cpuid_table->count) {
+		pr_info("Using SNP CPUID table, %d entries present.\n",
+			cpuid_table->count);
 
-	pr_info("Using SNP CPUID table, %d entries present.\n",
-		cpuid_table->count);
+		if (sev_cfg.debug)
+			dump_cpuid_table();
+	}
 
-	if (sev_cfg.debug)
-		dump_cpuid_table();
+	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		pr_info("SNP running at VMPL%u.\n", snp_vmpl);
 
 	return 0;
 }
-arch_initcall(report_cpuid_table);
+arch_initcall(report_snp_info);
 
 static int __init init_sev_config(char *str)
 {