linux-kernel - Re: [PATCH] x86/microcode: Refactor Intel microcode loading

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Date:   Fri, 5 Apr 2019 06:10:28 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jann Horn <jannh@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH] x86/microcode: Refactor Intel microcode loading

On Fri, Apr 05, 2019 at 12:54:31AM +0200, Jann Horn wrote:
> [  159.485731] microcode: CPU7 found a matching microcode update with
> version 0x25 (current=0x19)

Yeah, that printk can be kinda misleading :)

> I thought I had checked /sys/devices/system/cpu/cpu0/microcode/version
> afterwards. But apparently I didn't. Bleh. Sorry about that.

No worries at all, now at least it is all clear what's happening. I was
beginning to recheck what I'm seeing here too.

And I can finally deprecate this ancient method which is just as
kaputtski because it is happening as late as the late loading method
when you do

echo 1 > /sys/devices/system/cpu/microcode/reload

---
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5ad92419be19..5a0a752f3ddd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1330,8 +1330,16 @@ config MICROCODE_AMD
 	  processors will be enabled.
 
 config MICROCODE_OLD_INTERFACE
-	def_bool y
+	bool "Ancient loading interface (DEPRECATED)"
+	default n
 	depends on MICROCODE
+	---help---
+	  DO NOT USE THIS! This is the ancient /dev/cpu/microcode interface
+	  which was used by userspace tools like iucode_tool and microcode.ctl.
+	  It is inadequate because it runs too late to be able to properly
+	  load microcode on a machine and it needs special tools. Instead, you
+	  should've switched to the early loading method with the initrd or
+	  builtin microcode by now: Documentation/x86/microcode.txt
 
 config X86_MSR
 	tristate "/dev/cpu/*/msr - Model-specific register support"
---

I'll test some more and post later.

Thx!

-- 
Regards/Gruss,
    Boris.

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