[PATCH] x86/microcode: Remove useless code after early microcode support added

[PATCH] x86/microcode: Remove useless code after early microcode support added

[Zhenzhong Duan]

After early microcode update was added, microcode couldn't be configured
as a module, microcode update happens at early bootup and cpu hotplug
stage. This made the microcode update code in module loading stage
useless.

This patch remove the useless code.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Srinivas Eeda <srinivas.eeda@oracle.com>
---
 arch/x86/kernel/cpu/microcode/core.c | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 5260185..7f05bcb 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -710,10 +710,6 @@ static enum ucode_state microcode_init_cpu(int cpu, bool refresh_fw)
 	if (collect_cpu_info(cpu))
 		return UCODE_ERROR;
 
-	/* --dimm. Trigger a delayed update? */
-	if (system_state != SYSTEM_RUNNING)
-		return UCODE_NFOUND;
-
 	ustate = microcode_ops->request_microcode_fw(cpu, &microcode_pdev->dev, refresh_fw);
 	if (ustate == UCODE_NEW) {
 		pr_debug("CPU%d updated upon init\n", cpu);
@@ -738,21 +734,14 @@ static enum ucode_state microcode_update_cpu(int cpu)
 
 static int mc_device_add(struct device *dev, struct subsys_interface *sif)
 {
-	int err, cpu = dev->id;
+	int cpu = dev->id;
 
 	if (!cpu_online(cpu))
 		return 0;
 
 	pr_debug("CPU%d added\n", cpu);
 
-	err = sysfs_create_group(&dev->kobj, &mc_attr_group);
-	if (err)
-		return err;
-
-	if (microcode_init_cpu(cpu, true) == UCODE_ERROR)
-		return -EINVAL;
-
-	return err;
+	return sysfs_create_group(&dev->kobj, &mc_attr_group);
 }
 
 static void mc_device_remove(struct device *dev, struct subsys_interface *sif)
-- 
1.8.3.1

Re: [PATCH] x86/microcode: Remove useless code after early microcode support added

[Borislav Petkov]

On Mon, Apr 01, 2019 at 04:46:52PM +0800, Zhenzhong Duan wrote:
> After early microcode update was added, microcode couldn't be configured

No, early loading doesn't have anything to do with it - the driver was
made built-in only.

> as a module, microcode update happens at early bootup and cpu hotplug
> stage. This made the microcode update code in module loading stage
> useless.
> 
> This patch

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

> remove the useless code.

Well, not useless.

1. Apply your patch, boot kernel without an initrd so that it doesn't
apply early microcode.

2. Load late microcode:

# echo 1 > /sys/devices/system/cpu/microcode/reload
[   66.430052] microcode: CPU0: new patch_level=0x05000029
[   66.430352] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
[   66.430620] microcode: Reload completed, microcode revision: 0x5000029

3.
# grep microcode /proc/cpuinfo
microcode       : 0x5000029
microcode       : 0x5000028	<--- !!!

Whoops. CPU1 didn't get updated.

So I'd suggest leaving this code alone and concentrating on fixing real
bugs. Unless it is causing other issues.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Re: [PATCH] x86/microcode: Remove useless code after early microcode support added

[Borislav Petkov]

On Wed, Apr 03, 2019 at 03:40:24PM +0800, Zhenzhong Duan wrote:
> I remember microcode could be module before early loading was added.

You've remembered it wrongly, it is the other way around:

9a2bc335f100 ("x86/microcode: Unmodularize the microcode driver")

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.