[svsm-devel] [PATCH v4 15/15] x86/sev: Allow non-VMPL0 execution when an SVSM is present

[Tom Lendacky]

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.

Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
---
 arch/x86/boot/compressed/sev.c    | 12 +++++++++---
 arch/x86/include/asm/sev-common.h |  1 +
 arch/x86/kernel/sev.c             | 20 +++++++++++++++++---
 3 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 32a1e98ffaa9..fb1e60165cd1 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -610,11 +610,13 @@ 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 = 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.
 		 *
 		 * RMPADJUST modifies RMP permissions of a lesser-privileged (numerically
 		 * higher) privilege level. Here, clear the VMPL1 permission mask of the
@@ -624,8 +626,12 @@ void sev_enable(struct boot_params *bp)
 		 * modifies permission bits, it is still ok to do so currently because Linux
 		 * SNP guests running at VMPL0 only run at VMPL0, so VMPL1 or higher
 		 * permission mask changes are a don't-care.
+		 *
+		 * Running at VMPL0 is not required if an SVSM is present and the hypervisor
+		 * supports the required SVSM GHCB events.
 		 */
-		if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1))
+		if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1) &&
+		    !(vmpl && (hv_features & GHCB_HV_FT_SNP_MULTI_VMPL)))
 			sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
 	}
 
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 4cc716660d4b..7a9d09458989 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -118,6 +118,7 @@ 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
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 5e71c94b952c..50754cc45161 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2356,22 +2356,36 @@ static void dump_cpuid_table(void)
  * sort of indicator, and there's not really any other good place to do it,
  * so do it here.
  */
-static int __init report_cpuid_table(void)
+static void __init report_cpuid_table(void)
 {
 	const struct snp_cpuid_table *cpuid_table = snp_cpuid_get_table();
 
 	if (!cpuid_table->count)
-		return 0;
+		return;
 
 	pr_info("Using SNP CPUID table, %d entries present.\n",
 		cpuid_table->count);
 
 	if (sev_cfg.debug)
 		dump_cpuid_table();
+}
+
+static void __init report_vmpl_level(void)
+{
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return;
+
+	pr_info("SNP running at VMPL%u.\n", vmpl);
+}
+
+static int __init report_snp_info(void)
+{
+	report_vmpl_level();
+	report_cpuid_table();
 
 	return 0;
 }
-arch_initcall(report_cpuid_table);
+arch_initcall(report_snp_info);
 
 static int __init init_sev_config(char *str)
 {
-- 
2.43.2