x86/microcode/AMD: Check patch level only on the BSP

Check final patch levels for AMD only on the BSP. This way, we decide
early and only once whether to continue loading or to leave the loader
disabled on such systems.

Simplify a lot.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/20170120202955.4091-13-bp@alien8.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 41 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index dc54518299c4..3b74d2f315d3 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -69,6 +69,42 @@ struct cpu_info_ctx {
 	int			err;
 };
 
+/*
+ * Those patch levels cannot be updated to newer ones and thus should be final.
+ */
+static u32 final_levels[] = {
+	0x01000098,
+	0x0100009f,
+	0x010000af,
+	0, /* T-101 terminator */
+};
+
+/*
+ * Check the current patch level on this CPU.
+ *
+ * Returns:
+ *  - true: if update should stop
+ *  - false: otherwise
+ */
+static bool amd_check_current_patch_level(void)
+{
+	u32 lvl, dummy, i;
+	u32 *levels;
+
+	native_rdmsr(MSR_AMD64_PATCH_LEVEL, lvl, dummy);
+
+	if (IS_ENABLED(CONFIG_X86_32))
+		levels = (u32 *)__pa_nodebug(&final_levels);
+	else
+		levels = final_levels;
+
+	for (i = 0; levels[i]; i++) {
+		if (lvl == levels[i])
+			return true;
+	}
+	return false;
+}
+
 static bool __init check_loader_disabled_bsp(void)
 {
 	static const char *__dis_opt_str = "dis_ucode_ldr";
@@ -95,6 +131,11 @@ static bool __init check_loader_disabled_bsp(void)
 	if (native_cpuid_ecx(1) & BIT(31))
 		return *res;
 
+	if (x86_cpuid_vendor() == X86_VENDOR_AMD) {
+		if (amd_check_current_patch_level())
+			return *res;
+	}
+
 	if (cmdline_find_option_bool(cmdline, option) <= 0)
 		*res = false;