Re: [PATCH v3 2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests

[David Hildenbrand]

On 16.04.24 08:37, Alexander Gordeev wrote:
> On Mon, Apr 15, 2024 at 09:14:03PM +0200, David Hildenbrand wrote:
> > > > +retry:
> > > > +		rc = walk_page_range_vma(vma, addr, vma->vm_end,
> > > > +					 &find_zeropage_ops, &addr);
> > > > +		if (rc <= 0)
> > > > +			continue;
> > >
> > > So in case an error is returned for the last vma, __s390_unshare_zeropage()
> > > finishes with that error. By contrast, the error for a non-last vma would
> > > be ignored?
> >
> > Right, it looks a bit off. walk_page_range_vma() shouldn't fail
> > unless find_zeropage_pte_entry() would fail -- which would also be
> > very unexpected.
> >
> > To handle it cleanly in case we would ever get a weird zeropage where we
> > don't expect it, we should probably just exit early.
> >
> > Something like the following (not compiled, addressing the comment below):
>
> > @@ -2618,7 +2618,8 @@ static int __s390_unshare_zeropages(struct mm_struct *mm)
> >   	struct vm_area_struct *vma;
> >   	VMA_ITERATOR(vmi, mm, 0);
> >   	unsigned long addr;
> > -	int rc;
> > +	vm_fault_t rc;
> > +	int zero_page;
>
> I would use "fault" for mm faults (just like everywhere else handle_mm_fault() is
> called) and leave rc as is:
>
> 	vm_fault_t fault;
> 	int rc;

Sure, let me know once discussion here stopped whether you want a v4 or 
can fix that up.

--
Cheers,

David / dhildenb