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

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Message-ID: <c7f895b1-4f48-4d41-91ed-26ca857e3665@kernel.org>
Date: Mon, 21 Jul 2025 13:13:27 -0500
From: Mario Limonciello <superm1@...nel.org>
To: Yazen Ghannam <yazen.ghannam@....com>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org, Libing He <libhe@...hat.com>,
 David Arcari <darcari@...hat.com>
Subject: Re: [PATCH] x86/CPU/AMD: Ignore invalid reset reason value

On 7/21/25 1:11 PM, Yazen Ghannam 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.
> 
> 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
Reviewed-by: Mario Limonciello <mario.limonciello@....com>

> ---
>   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