Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

Christoph Hellwig
2020-04-08T05:18:49Z

On Tue, Apr 07, 2020 at 11:27:54PM +0200, Peter Zijlstra wrote:
> On Tue, Apr 07, 2020 at 02:22:11PM -0700, Nadav Amit wrote:
> > Anyhow, I do not think it is the only use-case which is not covered by your
> > patches (even considering CRs/DRs alone). For example, there is no kernel
> > function to turn on CR4.VMXE, which is required to run hypervisors on x86.
>
> That needs an exported function; there is no way we'll allow random
> writes to CR4, there's too much dodgy stuff in there.

And this clearly shows while trying to cater to anyone doing hardware
virt out of tree is just a disaster and we need to stick to our
traditional line that out of tree modules don't matter, if you care
about your module bring it upstream. Especially as we have a perfectly
fine upstream module for just about every variant of hardware
virtualization that can be extended for the needs of other hypervisors.