Re: [PATCH v12 05/31] mm: prepare for FAULT_FLAG_SPECULATIVE

[Laurent Dufour]

Le 19/04/2019 Ã 00:04, Jerome Glisse a ÃcritÂ:
> On Tue, Apr 16, 2019 at 03:44:56PM +0200, Laurent Dufour wrote:
> > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> >
> > When speculating faults (without holding mmap_sem) we need to validate
> > that the vma against which we loaded pages is still valid when we're
> > ready to install the new PTE.
> >
> > Therefore, replace the pte_offset_map_lock() calls that (re)take the
> > PTL with pte_map_lock() which can fail in case we find the VMA changed
> > since we started the fault.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> >
> > [Port to 4.12 kernel]
> > [Remove the comment about the fault_env structure which has been
> >   implemented as the vm_fault structure in the kernel]
> > [move pte_map_lock()'s definition upper in the file]
> > [move the define of FAULT_FLAG_SPECULATIVE later in the series]
> > [review error path in do_swap_page(), do_anonymous_page() and
> >   wp_page_copy()]
> > Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
>
> Reviewed-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
>
> > ---
> >   mm/memory.c | 87 +++++++++++++++++++++++++++++++++++------------------
> >   1 file changed, 58 insertions(+), 29 deletions(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index c6ddadd9d2b7..fc3698d13cb5 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -2073,6 +2073,13 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
> >   }
> >   EXPORT_SYMBOL_GPL(apply_to_page_range);
> >   
> > +static inline bool pte_map_lock(struct vm_fault *vmf)
>
> I am not fan of the name maybe pte_offset_map_lock_if_valid() ? But
> that just a taste thing. So feel free to ignore this comment.

I agree with you that adding _if_valid or something equivalent to 
highlight the conditional of this function would be a good idea.

I'll think further about that name but yours looks good ;)


> > +{
> > +	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
> > +				       vmf->address, &vmf->ptl);
> > +	return true;
> > +}
> > +
> >   /*
> >    * handle_pte_fault chooses page fault handler according to an entry which was
> >    * read non-atomically.  Before making any commitment, on those architectures