linux-kernel - Re: [PATCH v2] x86/CPU/AMD: Ignore invalid reset reason value

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Message-ID: <61E4BD23-24B4-42E0-834F-1E1E416EFA34@alien8.de>
Date: Thu, 24 Jul 2025 07:25:58 +0300
From: Borislav Petkov <bp@...en8.de>
To: Yazen Ghannam <yazen.ghannam@....com>, x86@...nel.org
CC: linux-kernel@...r.kernel.org, Libing He <libhe@...hat.com>,
 Mario Limonciello <mario.limonciello@....com>,
 David Arcari <darcari@...hat.com>
Subject: Re: [PATCH v2] x86/CPU/AMD: Ignore invalid reset reason value

On July 23, 2025 11:07:52 PM GMT+03:00, Yazen Ghannam <yazen.ghannam@....com> wrote:
>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.
>
>Return early if running in a VM as this register is not emulated.
>
>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>
>Reviewed-by: Mario Limonciello <mario.limonciello@....com>
>Cc: David Arcari <darcari@...hat.com>
>Cc: stable@...r.kernel.org
>---
>Link:
>https://lore.kernel.org/r/20250721181155.3536023-1-yazen.ghannam@amd.com
>
>v1->v2:
>* Include Reviewed-by tag from Mario.
>* Include hypervisor check suggested by Boris.
>
> arch/x86/kernel/cpu/amd.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
>index 50f88fe51816..7a10fe426104 100644
>--- a/arch/x86/kernel/cpu/amd.c
>+++ b/arch/x86/kernel/cpu/amd.c
>@@ -1274,10 +1274,13 @@ 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_HYPERVISOR))
>+		return 0;
>+
> 	if (!cpu_feature_enabled(X86_FEATURE_ZEN))
> 		return 0;
> 
>@@ -1288,12 +1291,16 @@ 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

Ack.
-- 
Sent from a small device: formatting sucks and brevity is inevitable.