x86/sev: Add a sev= cmdline option

For debugging purposes it is very useful to have a way to see the full
contents of the SNP CPUID table provided to a guest. Add an sev=debug
kernel command-line option to do so.

Also introduce some infrastructure so that additional options can be
specified via sev=option1[,option2] over time in a consistent manner.

  [ bp: Massage, simplify string parsing. ]
Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-41-brijesh.singh@amd.com

Documentation/admin-guide/kernel-parameters.txt

@@ -5308,6 +5308,8 @@
 
 	serialnumber	[BUGS=X86-32]
 
+	sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst
+
 	shapers=	[NET]
 			Maximal number of shapers.
 

Documentation/x86/x86_64/boot-options.rst

@@ -310,3 +310,17 @@ Miscellaneous
     Do not use GB pages for kernel direct mappings.
   gbpages
     Use GB pages for kernel direct mappings.
+
+
+AMD SEV (Secure Encrypted Virtualization)
+=========================================
+Options relating to AMD SEV, specified via the following format:
+
+::
+
+   sev=option1[,option2]
+
+The available options are:
+
+   debug
+     Enable debug messages.

arch/x86/kernel/sev.c

@@ -112,6 +112,13 @@ DEFINE_STATIC_KEY_FALSE(sev_es_enable_key);
 
 static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
 
+struct sev_config {
+	__u64 debug		: 1,
+	      __reserved	: 63;
+};
+
+static struct sev_config sev_cfg __read_mostly;
+
 static __always_inline bool on_vc_stack(struct pt_regs *regs)
 {
 	unsigned long sp = regs->sp;
@@ -2042,6 +2049,23 @@ void __init snp_abort(void)
 	sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
 }
 
+static void dump_cpuid_table(void)
+{
+	const struct snp_cpuid_table *cpuid_table = snp_cpuid_get_table();
+	int i = 0;
+
+	pr_info("count=%d reserved=0x%x reserved2=0x%llx\n",
+		cpuid_table->count, cpuid_table->__reserved1, cpuid_table->__reserved2);
+
+	for (i = 0; i < SNP_CPUID_COUNT_MAX; i++) {
+		const struct snp_cpuid_fn *fn = &cpuid_table->fn[i];
+
+		pr_info("index=%3d fn=0x%08x subfn=0x%08x: eax=0x%08x ebx=0x%08x ecx=0x%08x edx=0x%08x xcr0_in=0x%016llx xss_in=0x%016llx reserved=0x%016llx\n",
+			i, fn->eax_in, fn->ecx_in, fn->eax, fn->ebx, fn->ecx,
+			fn->edx, fn->xcr0_in, fn->xss_in, fn->__reserved);
+	}
+}
+
 /*
  * It is useful from an auditing/testing perspective to provide an easy way
  * for the guest owner to know that the CPUID table has been initialized as
@@ -2059,6 +2083,26 @@ static int __init report_cpuid_table(void)
 	pr_info("Using SNP CPUID table, %d entries present.\n",
 		cpuid_table->count);
 
+	if (sev_cfg.debug)
+		dump_cpuid_table();
+
 	return 0;
 }
 arch_initcall(report_cpuid_table);
+
+static int __init init_sev_config(char *str)
+{
+	char *s;
+
+	while ((s = strsep(&str, ","))) {
+		if (!strcmp(s, "debug")) {
+			sev_cfg.debug = true;
+			continue;
+		}
+
+		pr_info("SEV command-line option '%s' was not recognized\n", s);
+	}
+
+	return 1;
+}
+__setup("sev=", init_sev_config);