linux-kernel - [PATCH v2 14/14] x86/sev: Allow non-VMPL0 execution when an SVSM is present

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Date: Fri, 8 Mar 2024 12:35:29 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: <linux-kernel@...r.kernel.org>, <x86@...nel.org>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, "Peter
 Zijlstra" <peterz@...radead.org>, Dan Williams <dan.j.williams@...el.com>,
	Michael Roth <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>
Subject: [PATCH v2 14/14] 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.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/boot/compressed/sev.c    | 11 +++++++++--
 arch/x86/include/asm/sev-common.h |  1 +
 arch/x86/kernel/sev.c             | 20 +++++++++++++++++---
 3 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 89143f0aedb6..0f9c6f41caf1 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -619,10 +619,17 @@ 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);
 
-		if (!running_at_vmpl0(&boot_ghcb_page))
+		/*
+		 * VMPL0 is not required if an SVSM is present and the hypervisor
+		 * supports the required SVSM GHCB events.
+		 */
+		if (!running_at_vmpl0(&boot_ghcb_page) &&
+		    !(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 71db5ba020b9..3de377a4e981 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 4e460d9eba77..8ae962127989 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2368,22 +2368,36 @@ 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