Patch "x86/microcode: Do the family check first" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

x86/microcode: Do the family check first

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-microcode-do-the-family-check-first.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Borislav Petkov <[email protected]>
Date: Thu, 12 Oct 2017 13:23:16 +0200
Subject: x86/microcode: Do the family check first

From: Borislav Petkov <[email protected]>

commit 1f161f67a272cc4f29f27934dd3f74cb657eb5c4 upstream.

On CPUs like AMD's Geode, for example, we shouldn't even try to load microcode because they do not support the modern microcode loading interface.

However, we do the family check *after* the other checks whether the loader has been disabled on the command line or whether we're running in a guest.

So move the family checks first in order to exit early if we're being loaded on an unsupported family.

---
 arch/x86/kernel/cpu/microcode/core.c |   27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

@@ -122,9 +122,6 @@ static bool __init check_loader_disabled
 	bool *res = &dis_ucode_ldr;
 #endif
 
-	if (!have_cpuid_p())
-		return *res;
-
 	/*
 	 * CPUID(1).ECX[31]: reserved for hypervisor use. This is still not
 	 * completely accurate as xen pv guests don't see that CPUID bit set but

@@ -166,24 +163,36 @@ bool get_builtin_firmware(struct cpio_da
 void __init load_ucode_bsp(void)
 {
 	unsigned int cpuid_1_eax;
+	bool intel = true;
 
-	if (check_loader_disabled_bsp())
+	if (!have_cpuid_p())
 		return;
 
 	cpuid_1_eax = native_cpuid_eax(1);
 
 	switch (x86_cpuid_vendor()) {
 	case X86_VENDOR_INTEL:
-		if (x86_family(cpuid_1_eax) >= 6)
-			load_ucode_intel_bsp();
+		if (x86_family(cpuid_1_eax) < 6)
+			return;
 		break;
+
 	case X86_VENDOR_AMD:
-		if (x86_family(cpuid_1_eax) >= 0x10)
-			load_ucode_amd_bsp(cpuid_1_eax);
+		if (x86_family(cpuid_1_eax) < 0x10)
+			return;
+		intel = false;
 		break;
+
 	default:
-		break;
+		return;
 	}
+
+	if (check_loader_disabled_bsp())
+		return;
+
+	if (intel)
+		load_ucode_intel_bsp();
+	else
+		load_ucode_amd_bsp(cpuid_1_eax);
 }
 
 static bool check_loader_disabled_ap(void)

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/x86-microcode-do-the-family-check-first.patch queue-4.13/x86-alternatives-fix-alt_max_short-macro-to-really-be-a-max.patch queue-4.13/ras-cec-use-the-right-length-for-cec_disable.patch