linux-kernel - [PATCH] x86/CPU/AMD: Ignore invalid reset reason value

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Message-ID: <20250721181155.3536023-1-yazen.ghannam@amd.com>
Date: Mon, 21 Jul 2025 18:11:54 +0000
From: Yazen Ghannam <yazen.ghannam@....com>
To: <x86@...nel.org>
CC: <linux-kernel@...r.kernel.org>, Yazen Ghannam <yazen.ghannam@....com>,
	Libing He <libhe@...hat.com>, David Arcari <darcari@...hat.com>, "Mario
 Limonciello" <mario.limonciello@....com>
Subject: [PATCH] x86/CPU/AMD: Ignore invalid reset reason value

The reset reason value may be "all bits set", e.g. 0xFFFFFFFF. This is a
commonly used error response from hardware. This may occur due to a real
hardware issue or when running in a VM.

The user will see all reset reasons reported in this case.

Check for an error response value and return early to avoid decoding
invalid data.

Also, adjust the data variable type to match the hardware register size.

Fixes: ab8131028710 ("x86/CPU/AMD: Print the reason for the last reset")
Reported-by: Libing He <libhe@...hat.com>
Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
Cc: David Arcari <darcari@...hat.com>
Cc: Mario Limonciello <mario.limonciello@....com>
Cc: stable@...r.kernel.org
---
 arch/x86/kernel/cpu/amd.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 50f88fe51816..db0f9e0d181a 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1274,8 +1274,8 @@ static const char * const s5_reset_reason_txt[] = {
 
 static __init int print_s5_reset_status_mmio(void)
 {
-	unsigned long value;
 	void __iomem *addr;
+	u32 value;
 	int i;
 
 	if (!cpu_feature_enabled(X86_FEATURE_ZEN))
@@ -1288,12 +1288,16 @@ static __init int print_s5_reset_status_mmio(void)
 	value = ioread32(addr);
 	iounmap(addr);
 
+	/* Value with "all bits set" is an error response and should be ignored. */
+	if (value == U32_MAX)
+		return 0;
+
 	for (i = 0; i < ARRAY_SIZE(s5_reset_reason_txt); i++) {
 		if (!(value & BIT(i)))
 			continue;
 
 		if (s5_reset_reason_txt[i]) {
-			pr_info("x86/amd: Previous system reset reason [0x%08lx]: %s\n",
+			pr_info("x86/amd: Previous system reset reason [0x%08x]: %s\n",
 				value, s5_reset_reason_txt[i]);
 		}
 	}

base-commit: 65f55a30176662ee37fe18b47430ee30b57bfc98
-- 
2.50.1