x86/cpu/intel: Detect SGX support

x86/cpu/intel: Detect SGX support

Kernel support for SGX is ultimately decided by the state of the launch
control bits in the feature control MSR (MSR_IA32_FEAT_CTL).  If the
hardware supports SGX, but neglects to support flexible launch control, the
kernel will not enable SGX.

Enable SGX at feature control MSR initialization and update the associated
X86_FEATURE flags accordingly.  Disable X86_FEATURE_SGX (and all
derivatives) if the kernel is not able to establish itself as the authority
over SGX Launch Control.

All checks are performed for each logical CPU (not just boot CPU) in order
to verify that MSR_IA32_FEATURE_CONTROL is correctly configured on all
CPUs. All SGX code in this series expects the same configuration from all
CPUs.

This differs from VMX where X86_FEATURE_VMX is intentionally cleared only
for the current CPU so that KVM can provide additional information if KVM
fails to load like which CPU doesn't support VMX.  There’s not much the
kernel or an administrator can do to fix the situation, so SGX neglects to
convey additional details about these kinds of failures if they occur.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Jethro Beekman <jethro@fortanix.com>
Link: https://lkml.kernel.org/r/20201112220135.165028-8-jarkko@kernel.org