On Wed, 26 Feb 2014 19:06:03 +0100 Oleg Nesterov <[email protected]> wrote:
> On 02/26, Alex Thorlton wrote: > > > > + * MADV_HUGEPAGE after PRCTL_THP_DISABLE is broken on s390 because > > + * qemu blindly does madvise(MADV_HUGEPAGE) after s390_enable_sie(). > > + */ > > +#ifdef CONFIG_S390 > > + if (mm_has_pgste(vma->vm_mm)) > > return -EINVAL; > > +#endif > > The comment is not really right... > > And personally I think that > > @@ -504,6 +504,9 @@ static int gmap_connect_pgtable(unsigned long > address, unsigned long segment, > if (!pmd_present(*pmd) && > __pte_alloc(mm, vma, pmd, vmaddr)) > return -ENOMEM; > + /* large pmds cannot yet be handled */ > + if (pmd_large(*pmd)) > + return -EFAULT; > > change still makes sense, so that we can simply revert this s390- > specific hack in hugepage_madvise(). Yes, agreed. > > I'd suggest the patch below on top of your changes, but I won't argue. > > It would be nice to also change thp_split_mm() to not not play with > mm->def_flags, but I am not sure if we can do this. Hmm, I'm also wondering about this. Basically, we only need VM_NOHUGEPAGE in vma->vm_flags, which is done for all existing vmas in thp_split_mm(). But if there should be new vmas created afterwards, it would still be necessary to also have VM_NOHUGEPAGE in mm->def_flags, because the vm_flags for new vmas will be set via OR of mm->def_flags, e.g. in do_brk() and do_mmap_pgoff(). I guess the question is if new vmas can be created for the qemu/kvm host process? Anyway, this would then have to be a separate patch, to keep the "revertability" of this hack. > > Oleg. > --- > > Subject: [PATCH] s390: make sure MADV_HUGEPAGE fails after s390_enable_sie() > > As Christian pointed out, the recent 'Revert "thp: make MADV_HUGEPAGE > check for mm->def_flags"' breaks qemu, it does QEMU_MADV_HUGEPAGE for > all kvm pages but this doesn't work after s390_enable_sie/thp_split_mm. > > Reported-by: Christian Borntraeger <[email protected]> > Suggested-by: Christian Borntraeger <[email protected]> > Signed-off-by: Oleg Nesterov <[email protected]> > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index a4310a5..0e08d92 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1970,11 +1970,22 @@ int hugepage_madvise(struct vm_area_struct *vma, > { > switch (advice) { > case MADV_HUGEPAGE: > +#ifdef CONFIG_S390 > + /* > + * MADV_HUGEPAGE is broken after s390_enable_sie(), qemu > + * blindly does madvise(MADV_HUGEPAGE) for for all kvm pages > + * and expects it must fail on s390. Avoid a possible SIGSEGV > + * until qemu is changed. > + */ > + if (mm_has_pgste(vma->vm_mm)) > + return -EINVAL; > +#endif > /* > * Be somewhat over-protective like KSM for now! > */ > if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP)) > return -EINVAL; > + > *vm_flags &= ~VM_NOHUGEPAGE; > *vm_flags |= VM_HUGEPAGE; > /* > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
