Re: [RFC PATCH] x86/split_lock: Disable SLD if an unaware (out-of-tree) module enables VMX

[Christoph Hellwig]

On Fri, Apr 03, 2020 at 09:30:07AM -0700, Sean Christopherson wrote:
> Hook into native CR4 writes to disable split-lock detection if CR4.VMXE
> is toggled on by an SDL-unaware entity, e.g. an out-of-tree hypervisor
> module.  Most/all VMX-based hypervisors blindly reflect #AC exceptions
> into the guest, or don't intercept #AC in the first place.  With SLD
> enabled, this results in unexpected #AC faults in the guest, leading to
> crashes in the guest and other undesirable behavior.

Out of tree modules do not matter, so we should not add code just to
work around broken third party code.  If you really feel strongly just
make sure something they rely on for their hacks stops being exported
and they are properly broken.