x86/cpufeature: Add facility to check for min microcode revisions

For bug workarounds or checks, it is useful to check for specific
microcode revisions.

Add a new generic function to match the CPU with stepping.
Add the other function to check the min microcode revisions for
the matched CPU.

A new table format is introduced to facilitate the quirk to
fill the related information.

This does not change the existing x86_cpu_id because it's an ABI
shared with modules, and also has quite different requirements,
as in no wildcards, but everything has to be matched exactly.

Originally-by: Andi Kleen <[e-mail]>
Suggested-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Kan Liang <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Acked-by: Borislav Petkov <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: [e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/include/asm/cpu_device_id.h

···
 
 extern const struct x86_cpu_id *x86_match_cpu(const struct x86_cpu_id *match);
 
+/*
+ * Match specific microcode revisions.
+ *
+ * vendor/family/model/stepping must be all set.
+ *
+ * Only checks against the boot CPU.  When mixed-stepping configs are
+ * valid for a CPU model, add a quirk for every valid stepping and
+ * do the fine-tuning in the quirk handler.
+ */
+
+struct x86_cpu_desc {
+	__u8	x86_family;
+	__u8	x86_vendor;
+	__u8	x86_model;
+	__u8	x86_stepping;
+	__u32	x86_microcode_rev;
+};
+
+#define INTEL_CPU_DESC(mod, step, rev) {			\
+	.x86_family = 6,					\
+	.x86_vendor = X86_VENDOR_INTEL,				\
+	.x86_model = mod,					\
+	.x86_stepping = step,					\
+	.x86_microcode_rev = rev,				\
+}
+
+extern bool x86_cpu_has_min_microcode_rev(const struct x86_cpu_desc *table);
+
 #endif

arch/x86/kernel/cpu/match.c

···
 	return NULL;
 }
 EXPORT_SYMBOL(x86_match_cpu);
+
+static const struct x86_cpu_desc *
+x86_match_cpu_with_stepping(const struct x86_cpu_desc *match)
+{
+	struct cpuinfo_x86 *c = &boot_cpu_data;
+	const struct x86_cpu_desc *m;
+
+	for (m = match; m->x86_family | m->x86_model; m++) {
+		if (c->x86_vendor != m->x86_vendor)
+			continue;
+		if (c->x86 != m->x86_family)
+			continue;
+		if (c->x86_model != m->x86_model)
+			continue;
+		if (c->x86_stepping != m->x86_stepping)
+			continue;
+		return m;
+	}
+	return NULL;
+}
+
+bool x86_cpu_has_min_microcode_rev(const struct x86_cpu_desc *table)
+{
+	const struct x86_cpu_desc *res = x86_match_cpu_with_stepping(table);
+
+	if (!res || res->x86_microcode_rev > boot_cpu_data.microcode)
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(x86_cpu_has_min_microcode_rev);