linux-kernel - Re: [Patch V1 2/7] x86/microcode/intel: Remove retries on early microcode load

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Date:   Mon, 5 Dec 2022 13:18:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ashok Raj <ashok.raj@...el.com>
Cc:     X86-kernel <x86@...nel.org>,
        LKML Mailing List <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>, alison.schofield@...el.com,
        reinette.chatre@...el.com
Subject: Re: [Patch V1 2/7] x86/microcode/intel: Remove retries on early
 microcode load

On Tue, Nov 29, 2022 at 01:08:27PM -0800, Ashok Raj wrote:
> There is no direct evidence that these end user issues were caused by this
> retry loop. However, the early boot hangs along with reverting the
> microcode update workaround provide strong circumstantial evidence to
> support the theory that they are linked.

A "circumstantial" reason for why something "might" be broken has no
place in a commit message.

If you still wanna chase this and *actually* give me a sane,
comprehensible reason of why this could cause an endless loop with
officially released microcode, then I'm willing to listen.

Otherwise, I'll apply this:

---
From: Ashok Raj <ashok.raj@...el.com>
Date: Tue, 29 Nov 2022 13:08:27 -0800
Subject: x86/microcode/intel: Remove retries on early microcode load

The retries in load_ucode_intel_ap() were in place to support systems
with mixed steppings. Mixed steppings are no longer supported and there is
only one microcode image at a time. Any retries will simply reattempt to
apply the same image over and over without making progress.

Fixes: 06b8534cb728 ("x86/microcode: Rework microcode loading")
Signed-off-by: Ashok Raj <ashok.raj@...el.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20221129210832.107850-3-ashok.raj@intel.com
---
 arch/x86/kernel/cpu/microcode/intel.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 4f93875f57b4..d68b084a17e7 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -495,7 +495,6 @@ void load_ucode_intel_ap(void)
 	else
 		iup = &intel_ucode_patch;
 
-reget:
 	if (!*iup) {
 		patch = __load_ucode_intel(&uci);
 		if (!patch)
@@ -505,13 +504,7 @@ void load_ucode_intel_ap(void)
 	}
 
 	uci.mc = *iup;
-
-	if (apply_microcode_early(&uci, true)) {
-		/* Mixed-silicon system? Try to refetch the proper patch: */
-		*iup = NULL;
-
-		goto reget;
-	}
+	apply_microcode_early(&uci, true);
 }
 
 static struct microcode_intel *find_patch(struct ucode_cpu_info *uci)

-- 
2.34.1


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette