On Wed, Aug 21, 2019 at 01:35:04PM -0600, Alex Williamson wrote:
> On Wed, 21 Aug 2019 13:08:59 -0600
> Alex Williamson <alex.williamson@xxxxxxxxxx> wrote:
> > Does this suggests something is still fundamentally wrong with the
> > premise of this change or have I done something stupid?
>
> Seems the latter, particularly your comment that we're looking for
> pages pointing to the gfn range to be removed, not just those in the
> range. Slot gfn ranges like ffe00-ffe1f are getting reduced to 0-0 or
> c0000-c0000, zapping zero or c0000, and I think one of the ones you
> were looking for c1080-c1083 is reduce to c1000-c1000 and therefore
> zaps sp->gfn c1000. I'll keep looking. Thanks,
Ya. As far as where to look, at this point I don't think it's an issue of
incorrect zapping. Not because I'm 100% confident the zapping logic is
correct, but because many of the tests, e.g. removing 'sp->gfn != gfn' and
not being able to exclude APIC/IOAPIC ranges, suggest that the badness is
'fixed' by zapping seemingly unrelated sps.
In other words, it may be fundamentally wrong to zap only the memslot
being removed, but I really want to know why. History isn't helpful as
KVM has always zapped all pages when removing a memslot (on x86), and the
introduction of the per-memslot flush hook in commit
2df72e9bc4c5 ("KVM: split kvm_arch_flush_shadow")
was all about refactoring generic code, and doesn't have any information
on whether per-memslot flushing was actually tried for x86.
