On Mon, 2022-09-12 at 07:34 -0700, Dave Hansen wrote:
> On 9/12/22 07:31, Reinette Chatre wrote:
> >
> > On 9/12/2022 3:47 AM, Jarkko Sakkinen wrote:
> > > 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@xxxxxxxxx>
> > > Is it a pattern that flags are cleared when they are disabled by the
> > > kernel? I don't know the answer for this.
>
> There's no good pattern.
>
> But, one guideline is that the X86_FEATURE_*'s are for the *kernel*.
> They are *not* for userspace. The fact that the features are exposed to
> userspace in cpuinfo is unfortunate, but it doesn't change our guideline.
>
> So, if this patch is done only for the benefit of userspace, I don't
> think we should apply it.
It's not done for the userspace. AFAICT no one is complaining about this. I
just happened to see this and thought it's a right thing to do.
Also, in my other reply to this thread I put one reason that I think it's
reasonable:
"
But for SGX even the current upstream code clears SGX feature in some
conditions, for example, when SGX_LC is disabled by BIOS (in which case only KVM
SGX can be supported) and KVM SGX is also disabled, i.e. due to
CONFIG_X86_SGX_KVM isn't set:
if (!(msr & FEAT_CTL_SGX_LC_ENABLED) && enable_sgx_driver) {
if (!enable_sgx_kvm) {
pr_err_once("SGX Launch Control is locked. Disable SGX.\n");
clear_cpu_cap(c, X86_FEATURE_SGX);
else {
...
}
}
So I think it makes sense to clear SGX if both SGX driver and KVM SGX are not
enabled by the kernel.
"
--
Thanks,
-Kai
