linux-kernel - [PATCH v2] x86/CPU/AMD: Only apply Zenbleed fix for Zen2 during late microcode load

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Message-ID: <20240923164404.27227-1-john.allen@amd.com>
Date: Mon, 23 Sep 2024 16:44:04 +0000
From: John Allen <john.allen@....com>
To: <bp@...en8.de>, <x86@...nel.org>
CC: <linux-kernel@...r.kernel.org>, John Allen <john.allen@....com>,
	<stable@...r.kernel.org>
Subject: [PATCH v2] x86/CPU/AMD: Only apply Zenbleed fix for Zen2 during late microcode load

A problem was introduced with commit f69759be251d ("x86/CPU/AMD: Move
Zenbleed check to the Zen2 init function") where a bit in the DE_CFG MSR
is getting set after a microcode late load.

The problem seems to be that the microcode late load path calls into
amd_check_microcode() and subsequently zen2_zenbleed_check(). Since the
patch removes the cpu_has_amd_erratum() check from zen2_zenbleed_check(),
this will cause all non-Zen2 CPUs to go through the function and set
the bit in the DE_CFG MSR.

Call into the zenbleed fix path on Zen2 CPUs only.

Fixes: f69759be251d ("x86/CPU/AMD: Move Zenbleed check to the Zen2 init function")
Cc: <stable@...r.kernel.org>
Acked-by: Borislav Petkov (AMD) <bp@...en8.de>
Signed-off-by: John Allen <john.allen@....com>
---
v2:
  - Clean up commit description
---
 arch/x86/kernel/cpu/amd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 015971adadfc..368344e1394b 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1202,5 +1202,6 @@ void amd_check_microcode(void)
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
 		return;

-	on_each_cpu(zenbleed_check_cpu, NULL, 1);
+	if (boot_cpu_has(X86_FEATURE_ZEN2))
+		on_each_cpu(zenbleed_check_cpu, NULL, 1);
 }
-- 
2.34.1