Re: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND_ALWAYS

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Apr 06, 2020 at 03:09:51PM -0400, Vivek Goyal wrote:
> On Mon, Mar 09, 2020 at 09:22:15PM +0100, Peter Zijlstra wrote:
> > On Mon, Mar 09, 2020 at 08:05:18PM +0100, Thomas Gleixner wrote:
> > > Andy Lutomirski <luto@kernel.org> writes:
> > 
> > > > I'm okay with the save/restore dance, I guess.  It's just yet more
> > > > entry crud to deal with architecture nastiness, except that this
> > > > nastiness is 100% software and isn't Intel/AMD's fault.
> > > 
> > > And we can do it in C and don't have to fiddle with it in the ASM
> > > maze.
> > 
> > Right; I'd still love to kill KVM_ASYNC_PF_SEND_ALWAYS though, even if
> > we do the save/restore in do_nmi(). That is some wild brain melt. Also,
> > AFAIK none of the distros are actually shipping a PREEMPT=y kernel
> > anyway, so killing it shouldn't matter much.
> 
> It will be nice if we can retain KVM_ASYNC_PF_SEND_ALWAYS. I have another
> use case outside CONFIG_PREEMPT.
> 
> I am trying to extend async pf interface to also report page fault errors
> to the guest.

Then please start over and design a sane ParaVirt Fault interface. The
current one is utter crap.