Re: [PATCH 2/2] x86/cpu: Handle GUEST_MAXPHYADDR < HOST_MAXPHYADDR for hosts that don't support it

[Eduardo Habkost]

On Fri, Jul 10, 2020 at 09:22:42AM +0200, Paolo Bonzini wrote:
> On 09/07/20 21:13, Eduardo Habkost wrote:
> >> Doesn't this require intercepting MOV-to-CR3 when the guest is in PAE
> >> mode, so that the hypervisor can validate the high bits in the PDPTEs?
> > If the fix has additional overhead, is the additional overhead
> > bad enough to warrant making it optional?  Most existing
> > GUEST_MAXPHYADDR < HOST_MAXPHYADDR guests already work today
> > without the fix.
> 
> The problematic case is when host maxphyaddr is 52.  That case wouldn't
> work at all without the fix.

What can QEMU do to do differentiate "can't work at all without
the fix" from "not the best idea, but will probably work"?

-- 
Eduardo