Re: [PATCH] x86/cpu/centaur: Disable X86_FEATURE_FSGSBASE on Zhaoxin C4600

[Borislav Petkov]

On Sat, Feb 28, 2026 at 05:37:04PM +0000, Yao Zi wrote:
> Zhaoxin C4600, which names itself as CentaurHauls, claims
> X86_FEATURE_FSGSBASE support in CPUID, while execution of fsgsbase-
> related instructions fails with #UD exception. This will cause kernel
> to crash early in current_save_fsgs().
> 
> Let's disable the feature on this problematic CPU and warn the user
> about the quirk. x86_model_id is used to match the platform to avoid
> unexpectedly breaking other CentaurHauls cores with conflicting
> family/model ID.

Please use passive voice in your commit message: no "we" or "I", etc,
and describe your changes in imperative mood.

Also, pls read section "2) Describe your changes" in
Documentation/process/submitting-patches.rst for more details.

Also, see section "Changelog" in
Documentation/process/maintainer-tip.rst

> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Yao Zi <me@xxxxxxxx>
> ---
>  arch/x86/kernel/cpu/centaur.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/centaur.c b/arch/x86/kernel/cpu/centaur.c
> index 81695da9c524..3773784ba6a9 100644
> --- a/arch/x86/kernel/cpu/centaur.c
> +++ b/arch/x86/kernel/cpu/centaur.c
> @@ -108,6 +108,29 @@ static void early_init_centaur(struct cpuinfo_x86 *c)
>  	}
>  }
>  
> +/*
> + * Zhaoxin C4600 (family 6, model 15) names itself as CentaurHauls, it claims
> + * X86_FEATURE_FSGSBASE support in CPUID, while executing any fsgsbase-related
> + * instructions on it results in #UD.
> + */
> +static void fixup_zhaoxin_fsgsbase(struct cpuinfo_x86 *c)

s/fixup/disable/

> +{
> +	const char *name, *model_names[] = {
> +		"C-QuadCore C4600"
> +	};

Why is this an array with a single string in it?

> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(model_names); i++) {

So that you can loop once with it?

Silly.

> +		name = model_names[i];
> +
> +		if (!strncmp(c->x86_model_id, name, strlen(name))) {
> +			pr_warn_once("CPU has broken FSGSBASE support\n");
> +			setup_clear_cpu_cap(X86_FEATURE_FSGSBASE);
> +			return;
> +		}
> +	}
> +}

-- 
Regards/Gruss,
    Boris.

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