[PATCH v12 40/46] x86/sev: add sev=debug cmdline option to dump SNP CPUID table

Brijesh Singh
2022-03-07T21:39:17Z

From: Michael Roth <michael.roth@amd.com>

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.

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
.../admin-guide/kernel-parameters.txt | 2 +
Documentation/x86/x86_64/boot-options.rst | 14 +++++
arch/x86/kernel/sev.c | 58 +++++++++++++++++++
3 files changed, 74 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f5a27f067db9..809e8adc9bb2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5229,6 +5229,8 @@

serialnumber [BUGS=X86-32]

+ sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst
+
shapers= [NET]
Maximal number of shapers.

diff --git a/Documentation/x86/x86_64/boot-options.rst b/Documentation/x86/x86_64/boot-options.rst
index 07aa0007f346..66c970117f0e 100644
--- a/Documentation/x86/x86_64/boot-options.rst
+++ b/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 verbose debug messages.
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index c6b2e0c58255..0b70ebb6df1d 100644
--- a/arch/x86/kernel/sev.c
+++ b/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;
@@ -2045,6 +2052,23 @@ 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
@@ -2062,6 +2086,40 @@ 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 bool matches_option(const char *option, const char *arg, int arg_len)
+{
+ return strncmp(option, arg, max(arg_len, (int)strlen(option))) == 0;
+}
+
+static int __init init_sev_config(char *str)
+{
+ if ((*str) == '=')
+ str++;
+
+ while (*str) {
+ char *arg = str;
+ int arg_len;
+
+ while (*str && *str != ',')
+ str++;
+
+ arg_len = str - arg;
+ if (*str == ',')
+ str++;
+
+ if (matches_option("debug", arg, arg_len))
+ sev_cfg.debug = true;
+ else
+ pr_info("SEV command-line option '%.*s' was not recognized\n", arg_len, arg);
+ }
+
+ return 1;
+}
+__setup("sev", init_sev_config);
--
2.25.1