linux-kernel - Re: [PATCH] x86/intel: Clear SGX bit if both SGX driver and KVM SGX are not enabled

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Message-ID: <Yx8OTDwhqbgvGp4p@kernel.org>
Date:   Mon, 12 Sep 2022 13:47:40 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Kai Huang <kai.huang@...el.com>
Cc:     linux-sgx@...r.kernel.org, dave.hansen@...ux.intel.com,
        seanjc@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/intel: Clear SGX bit if both SGX driver and KVM SGX
 are not enabled

On Fri, Sep 09, 2022 at 08:08:53PM +1200, Kai Huang wrote:
> Currently on platform which has SGX enabled, if CONFIG_X86_SGX is not
> enabled, the X86_FEATURE_SGX is not cleared, resulting in /proc/cpuinfo
> shows "sgx" feature.  This is not desired.
> 
> Clear SGX feature bit if both SGX driver and KVM SGX are not enabled in
> init_ia32_feat_ctl().
> 
> Signed-off-by: Kai Huang <kai.huang@...el.com>

Is it a pattern that flags are cleared when they are disabled by the
kernel? I don't know the answer for this.

I could imagine that sometimes you might want to know whether the CPU
supports a feature, even if e.g. your distribution kernel does not.

There's of course other ways to answer such qeustion, e.g. by using
cpuid utility.

BR, Jarkko