linux-kernel - Re: [tip: x86/microcode] x86/microcode: Do not taint when late loading on AMD

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Date:   Tue, 11 Apr 2023 14:48:32 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org, x86@...nel.org
Subject: Re: [tip: x86/microcode] x86/microcode: Do not taint when late
 loading on AMD

On Sun, Mar 12, 2023 at 08:47:36PM -0000, tip-bot2 for Borislav Petkov (AMD) wrote:
> The following commit has been merged into the x86/microcode branch of tip:
> 
> Commit-ID:     09b951476df9eadf15f2acba7568fa35e4b2313b
> Gitweb:        https://git.kernel.org/tip/09b951476df9eadf15f2acba7568fa35e4b2313b
> Author:        Borislav Petkov (AMD) <bp@...en8.de>
> AuthorDate:    Fri, 03 Mar 2023 12:46:49 +01:00
> Committer:     Borislav Petkov (AMD) <bp@...en8.de>
> CommitterDate: Sun, 12 Mar 2023 21:32:51 +01:00
> 
> x86/microcode: Do not taint when late loading on AMD
> 
> Describe why the concurrency issues which late loading poses are not
> affecting AMD hardware, after discussing it with hw folks. Thus, do not
> taint when late loading on it.
> 
> Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
> Link: https://lore.kernel.org/r/20230303114649.18552-1-bp@alien8.de

Forgot to adjust the error message too. Updated patch coming up.

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 779f70547fb7..22cf57c899b6 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -440,9 +440,6 @@ static int microcode_reload_late(void)
 	int old = boot_cpu_data.microcode, ret;
 	struct cpuinfo_x86 prev_info;
 
-	pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n");
-	pr_err("You should switch to early loading, if possible.\n");
-
 	atomic_set(&late_cpus_in,  0);
 	atomic_set(&late_cpus_out, 0);
 
@@ -498,8 +495,11 @@ static ssize_t reload_store(struct device *dev,
 	if (ret == 0)
 		ret = size;
 
-	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
+	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
+		pr_err("Late microcode loading is dangerous and taints the kernel.\n");
+		pr_err("You should switch to early loading if possible.\n");
 		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+	}
 
 	return ret;
 }

-- 
Regards/Gruss,
    Boris.

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