Patch "x86/microcode/intel: Extend BDW late-loading with a revision check" has been added to the 4.4-stable tree

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

x86/microcode/intel: Extend BDW late-loading with a revision check

to the 4.4-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-intel-extend-bdw-late-loading-with-a-revision-check.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Jia Zhang <[email protected]>
Date: Mon, 1 Jan 2018 10:04:47 +0800
Subject: x86/microcode/intel: Extend BDW late-loading with a revision check

From: Jia Zhang <[email protected]>

commit b94b7373317164402ff7728d10f7023127a02b60 upstream.

Instead of blacklisting all model 79 CPUs when attempting a late microcode loading, limit that only to CPUs with microcode revisions < 0x0b000021 because only on those late loading may cause a system hang.

For such processors either:

a) a BIOS update which might contain a newer microcode revision

or

b) the early microcode loading method

should be considered.

Processors with revisions 0x0b000021 or higher will not experience such hangs.

For more details, see erratum BDF90 in document #334165 (Intel Xeon Processor E7-8800/4800 v4 Product Family Specification Update) from September 2017.

[ bp: Heavily massage commit message and pr_* statements. ]

---
 arch/x86/kernel/cpu/microcode/intel.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

@@ -994,9 +994,17 @@ static bool is_blacklisted(unsigned int
 {
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
 
-	if (c->x86 == 6 && c->x86_model == 79) {
-		pr_err_once("late loading on model 79 is disabled.\n");
-		return true;
+	/*
+	 * Late loading on model 79 with microcode revision less than 0x0b000021
+	 * may result in a system hang. This behavior is documented in item
+	 * BDF90, #334165 (Intel Xeon Processor E7-8800/4800 v4 Product Family).
+	 */
+	if (c->x86 == 6 &&
+	    c->x86_model == 79 &&
+	    c->x86_mask == 0x01 &&
+	    c->microcode < 0x0b000021) {
+		pr_err_once("Erratum BDF90: late loading with revision < 0x0b000021 (0x%x) disabled.\n", c->microcode);
+		pr_err_once("Please consider either early loading through initrd/built-in or a potential BIOS update.\n");
 	}
 
 	return false;

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

queue-4.4/x86-microcode-intel-extend-bdw-late-loading-with-a-revision-check.patch