Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU)

[Balbir Singh]

On Mon, Aug 20, 2018 at 09:52:19PM +0000, Woodhouse, David wrote:
> On Mon, 2018-08-20 at 14:48 -0700, Linus Torvalds wrote:
> > 
> > Of course, after the long (and entirely unrelated) discussion about
> > the TLB flushing bug we had, I'm starting to worry about my own
> > competence, and maybe I'm missing something really fundamental, and
> > the XPFO patches do something else than what I think they do, or my
> > "hey, let's use our Meltdown code" idea has some fundamental weakness
> > that I'm missing.
> 
> The interesting part is taking the user (and other) pages out of the
> kernel's 1:1 physmap.
> 
> It's the *kernel* we don't want being able to access those pages,
> because of the multitude of unfixable cache load gadgets.

I am missing why we need this since the kernel can't access
(SMAP) unless we go through to the copy/to/from interface
or execute any of the user pages. Is it because of the dependency
on the availability of those features?

Balbir Singh.