linux-kernel - [v2 01/13] x86/microcode/intel: Prevent printing updated microcode rev multiple times

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Date:   Thu,  3 Nov 2022 17:58:49 +0000
From:   Ashok Raj <ashok.raj@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     "LKML Mailing List" <linux-kernel@...r.kernel.org>,
        X86-kernel <x86@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan van de Ven <arjan.van.de.ven@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jacon Jun Pan <jacob.jun.pan@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Kai Huang <kai.huang@...el.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: [v2 01/13] x86/microcode/intel: Prevent printing updated microcode rev multiple times

Commit b6f86689d5b7 ("x86/microcode: Rip out the subsys interface gunk")
introduced a race where all CPUs follow this call chain:

microcode_init()->schedule_on_each_cpu(setup_online_cpu)->collect_cpu_info

This results in console spam where multiple CPUs print the signature.

[   33.688639] microcode: sig=0x50654, pf=0x80, revision=0x2006e05
[   33.688659] microcode: sig=0x50654, pf=0x80, revision=0x2006e05
[   33.688660] microcode: sig=0x50654, pf=0x80, revision=0x2006e05

Fix by making sure only boot CPU prints the message.

Fixes: b6f86689d5b7 ("x86/microcode: Rip out the subsys interface gunk")
Reported-by: Tony Luck <tony.luck@...el.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Ashok Raj <ashok.raj@...el.com>
---
 arch/x86/kernel/cpu/microcode/intel.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 8c35c70029bf..8f7f8dd6680e 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -680,6 +680,7 @@ void reload_ucode_intel(void)
 
 static int collect_cpu_info(int cpu_num, struct cpu_signature *csig)
 {
+	bool bsp = cpu_num == boot_cpu_data.cpu_index;
 	static struct cpu_signature prev;
 	struct cpuinfo_x86 *c = &cpu_data(cpu_num);
 	unsigned int val[2];
@@ -696,8 +697,7 @@ static int collect_cpu_info(int cpu_num, struct cpu_signature *csig)
 
 	csig->rev = c->microcode;
 
-	/* No extra locking on prev, races are harmless. */
-	if (csig->sig != prev.sig || csig->pf != prev.pf || csig->rev != prev.rev) {
+	if (bsp && csig->rev != prev.rev) {
 		pr_info("sig=0x%x, pf=0x%x, revision=0x%x\n",
 			csig->sig, csig->pf, csig->rev);
 		prev = *csig;
-- 
2.34.1