Patch "x86/microcode: Do not upload microcode if CPUs are offline" has been added to the 4.15-stable tree

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

x86/microcode: Do not upload microcode if CPUs are offline

to the 4.15-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-not-upload-microcode-if-cpus-are-offline.patch
and it can be found in the queue-4.15 subdirectory.

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

From: Ashok Raj <[email protected]>
Date: Wed, 28 Feb 2018 11:28:43 +0100
Subject: x86/microcode: Do not upload microcode if CPUs are offline

From: Ashok Raj <[email protected]>

commit 30ec26da9967d0d785abc24073129a34c3211777 upstream.

Avoid loading microcode if any of the CPUs are offline, and issue a warning. Having different microcode revisions on the system at any time is outright dangerous.

[ Borislav: Massage changelog. ]

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

@@ -486,6 +486,16 @@ static void __exit microcode_dev_exit(vo
 /* fake device for request_firmware */
 static struct platform_device	*microcode_pdev;
 
+static int check_online_cpus(void)
+{
+	if (num_online_cpus() == num_present_cpus())
+		return 0;
+
+	pr_err("Not all CPUs online, aborting microcode update.\n");
+
+	return -EINVAL;
+}
+
 static enum ucode_state reload_for_cpu(int cpu)
 {
 	struct ucode_cpu_info *uci = ucode_cpu_info + cpu;

@@ -519,7 +529,13 @@ static ssize_t reload_store(struct devic
 		return size;
 
 	get_online_cpus();
+
+	ret = check_online_cpus();
+	if (ret)
+		goto put;
+
 	mutex_lock(&microcode_mutex);
+
 	for_each_online_cpu(cpu) {
 		tmp_ret = reload_for_cpu(cpu);
 		if (tmp_ret > UCODE_NFOUND) {

@@ -538,6 +554,8 @@ static ssize_t reload_store(struct devic
 		microcode_check();
 
 	mutex_unlock(&microcode_mutex);
+
+put:
 	put_online_cpus();
 
 	if (!ret)

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

queue-4.15/x86-microcode-intel-check-microcode-revision-before-updating-sibling-threads.patch queue-4.15/x86-microcode-attempt-late-loading-only-when-new-microcode-is-present.patch queue-4.15/x86-microcode-propagate-return-value-from-updating-functions.patch queue-4.15/x86-cpu-check-cpu-feature-bits-after-microcode-upgrade.patch queue-4.15/x86-microcode-intel-writeback-and-invalidate-caches-before-updating-microcode.patch queue-4.15/x86-microcode-intel-look-into-the-patch-cache-first.patch queue-4.15/x86-microcode-request-microcode-on-the-bsp.patch queue-4.15/x86-microcode-get-rid-of-struct-apply_microcode_ctx.patch queue-4.15/x86-microcode-fix-cpu-synchronization-routine.patch queue-4.15/x86-microcode-synchronize-late-microcode-loading.patch queue-4.15/x86-microcode-do-not-upload-microcode-if-cpus-are-offline.patch queue-4.15/x86-cpu-add-a-microcode-loader-callback.patch