Re: [Patch v5 1/4] Remove SMEP bit from CR4_RESERVED_BITS

[Ingo Molnar <mingo@elte.hu>]

* Tian, Kevin <kevin.tian@intel.com> wrote:

> > From: Ingo Molnar
> > Sent: Monday, May 30, 2011 3:41 PM
> > 
> > 
> > * Yang, Wei Y <wei.y.yang@intel.com> wrote:
> > 
> > > This patch removes SMEP bit from CR4_RESERVED_BITS.
> > 
> > I'm wondering, what is the best-practice way for tools/kvm/ to set
> > SMEP for the guest kernel automatically, even if the guest kernel
> > itsef has not requested SMEP?
> > 
> 
> enabling SMEP w/o guest's knowledge can be problematic if the guest 
> is doing U/S 0->1 bit change w/o TLB invalidation, which is a 
> required action to ensure SMEP protection working correctly. Linux 
> versions known so far don't have this behavior because TLB 
> invalidation due to P bit change covers U/S 0->1 change. [...]

We'd like to use this in the 'kvm' tool:

  git clone git://github.com/penberg/linux-kvm master
  cd linux-kvm/tools/kvm/
  make -j

Which is only interested in Linux guests.

Thanks,

	Ingo