Re: [Qemu-devel] [PATCH v1 0/2] s390x/tcg: LAP support using immediate TLB invalidation

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 17 Oct 2017 11:22:19 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 17.10.2017 10:47, Cornelia Huck wrote:
> > On Mon, 16 Oct 2017 22:23:56 +0200
> > David Hildenbrand <david@redhat.com> wrote:
> >   
> >> Details about Low-Address Protection can be found in description of
> >> patch 1 and 2. It is basically a subpage protection of the first two
> >> pages of every address space (for which it is enabled).
> >>
> >> We can achieve this by simply directly invalidating the TLB entry and
> >> therefore forcing every write accesses onto these two pages into the slow
> >> path.
> >>
> >> With this patch, I can boot Linux just fine (which uses LAP). This also
> >> makes all related kvm-unit-tests that we have pass.  
> > 
> > Tested with a kernel based on the s390/features branch (4.14-rc2 + s390
> > patches) and the initrd from the debian installer, had udevd shot down
> > by the oomkiller. That happened only once, so it was probably an
> > unrelated fluke, but that combination worked well before.
> >   
> 
> Very unlikely, on invalid programming exceptions you would get a kernel
> panic, not run oom. (not saying it isn't possible, rather that it is
> very unlikely).

That's what I thought as well.

> 
> Can you reproduce with more memory? Have you enabled SMP? (little higher
> memory consumption)

SMP is on. I could not reproduce it again...

> 
> I am running (almost) the same setup with 500M and haven't observed any
> such thing.

...so I think it really is an unrelated fluke (and I'll simply make the
machine a bit larger).