linux-kernel - Re: [tip: x86/urgent] x86/CPU/AMD: Add RDSEED fix for Zen5

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Message-ID: <20251103142800.GFaQi78AgT-qjY30r3@fat_crate.local>
Date: Mon, 3 Nov 2025 15:28:00 +0100
From: Borislav Petkov <bp@...en8.de>
To: Peter Jung <ptr1337@...hyos.org>
Cc: linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
	stable@...r.kernel.org, Gregory Price <gourry@...rry.net>,
	x86@...nel.org
Subject: Re: [tip: x86/urgent] x86/CPU/AMD: Add RDSEED fix for Zen5

On Mon, Nov 03, 2025 at 02:59:11PM +0100, Peter Jung wrote:
> CachyOS is compiling the packages with -march=znver5 and the GCC compiler
> currently does pass RDSEED.

Yah, the compiler should not *pass* RDSEED, but issue code which checks
whether RDSEED is there. Otherwise what's the point of CPUID flags?!

I guess this should make those boxes boot but damn, that ain't right:

---
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 8e36964a7721..810be49dad31 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1044,8 +1044,7 @@ static void init_amd_zen5(struct cpuinfo_x86 *c)
 {
 	if (!x86_match_min_microcode_rev(zen5_rdseed_microcode)) {
 		clear_cpu_cap(c, X86_FEATURE_RDSEED);
-		msr_clear_bit(MSR_AMD64_CPUID_FN_7, 18);
-		pr_emerg_once("RDSEED32 is broken. Disabling the corresponding CPUID bit.\n");
+		WARN_ONCE(1, "RDSEED32 is broken. Disabling the corresponding CPUID bit.\n");
 	}
 }
 
> This patch results into that also Client CPUs (Strix Point, Granite Ridge),
> can not execute this. There has been a microcode fix deployed in
> linux-firmware for Turin, but no other microcode changes seen yet.
> 
> I think it would be possible to exclude clients or providing a fix for this.

Client fixes are getting ready but I can't tell you when they'll be there.

-- 
Regards/Gruss,
    Boris.

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