Re: [PATCH] x86/cpufeatures: SGX: Adjust the error message when BIOS does not support SGX

[Huang, Kai]

On Tue, 2024-07-30 at 10:49 +0800, WangYuli wrote:
> When SGX is not supported by the BIOS, we still output the error
> 'SGX disabled by BIOS', which can be confusing since there might not be
> an SGX-related option in the BIOS settings.

+linux-sgx list, Jarkko, Haitao.

This message is only printed when SGX is reported in CPUID but is not
enabled in the FEAT_CTL MSR.  I can only recall this can happen when the
BIOS actually provides an option for the user to turn on/off SGX, in
which case the current message is correct.

I could be wrong, but I don't recall I have met any machine that doesn't
have any SGX option in the BIOS but still reports SGX in the CPUID.  Can
you confirm this is the case?  

I don't see this is mentioned in the github link below which reports this
issue.  In fact, it says:

	非bug，主板bios关闭了SGX，正常内核提醒

.. which is

	Not bug, the motherboard BIOS disabled SGX, normal kernel
message

And the link also shows this issue is "closed".

Please clarify.

> 
> As a kernel, it's difficult for us to distinguish between the BIOS not
> supporting SGX and the BIOS supporting SGX but it's disabled.
> 
> Therefore, we should update the error message to
> 'SGX disabled or unsupported by BIOS' to make it easier for those reading
> kernel logs to understand what's happening.
> 
> Reported-by: Bo Wu <wubo@xxxxxxxxxxxxx>
> Link: https://github.com/linuxdeepin/developer-center/issues/10032
> Signed-off-by: Zelong Xiang <xiangzelong@xxxxxxxxxxxxx>
> Signed-off-by: WangYuli <wangyuli@xxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/feat_ctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
> index 1640ae76548f..4a4118784c13 100644
> --- a/arch/x86/kernel/cpu/feat_ctl.c
> +++ b/arch/x86/kernel/cpu/feat_ctl.c
> @@ -188,7 +188,7 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
>  update_sgx:
>  	if (!(msr & FEAT_CTL_SGX_ENABLED)) {
>  		if (enable_sgx_kvm || enable_sgx_driver)
> -			pr_err_once("SGX disabled by BIOS.\n");
> +			pr_err_once("SGX disabled or unsupported by BIOS.\n");
>  		clear_cpu_cap(c, X86_FEATURE_SGX);
>  		return;
>  	}