Re: [PATCH resend RFC 0/9] s390: fixes, cleanups and optimizations for page table walkers

[Christian Borntraeger]

Am 28.09.21 um 12:59 schrieb Heiko Carstens:
> On Thu, Sep 09, 2021 at 06:22:39PM +0200, David Hildenbrand wrote:
> > Resend because I missed ccing people on the actual patches ...
> >
> > RFC because the patches are essentially untested and I did not actually
> > try to trigger any of the things these patches are supposed to fix. It
> > merely matches my current understanding (and what other code does :) ). I
> > did compile-test as far as possible.
> >
> > After learning more about the wonderful world of page tables and their
> > interaction with the mmap_sem and VMAs, I spotted some issues in our
> > page table walkers that allow user space to trigger nasty behavior when
> > playing dirty tricks with munmap() or mmap() of hugetlb. While some issues
> > should be hard to trigger, others are fairly easy because we provide
> > conventient interfaces (e.g., KVM_S390_GET_SKEYS and KVM_S390_SET_SKEYS).
> >
> > Future work:
> > - Don't use get_locked_pte() when it's not required to actually allocate
> >    page tables -- similar to how storage keys are now handled. Examples are
> >    get_pgste() and __gmap_zap.
> > - Don't use get_locked_pte() and instead let page fault logic allocate page
> >    tables when we actually do need page tables -- also, similar to how
> >    storage keys are now handled. Examples are set_pgste_bits() and
> >    pgste_perform_essa().
> > - Maybe switch to mm/pagewalk.c to avoid custom page table walkers. For
> >    __gmap_zap() that's very easy.
> >
> > Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > Cc: Janosch Frank <frankja@xxxxxxxxxxxxx>
> > Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
> > Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> > Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
> > Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
> > Cc: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> > Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
> > Cc: Ulrich Weigand <Ulrich.Weigand@xxxxxxxxxx>
>
> For the whole series:
> Acked-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
>
> Christian, given that this is mostly about KVM I'd assume this should
> go via the KVM tree. Patch 6 (pci_mmio) is already upstream.

Right, I think I will queue this even without testing for now.
Claudio, is patch 7 ok for you with the explanation from David?