Messages in this thread | | | Date | Tue, 8 Aug 2017 12:42:01 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC v5 02/11] mm: Prepare for FAULT_FLAG_SPECULATIVE |
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On Tue, Aug 08, 2017 at 03:54:01PM +0530, Anshuman Khandual wrote: > On 06/16/2017 11:22 PM, Laurent Dufour wrote: > > From: Peter Zijlstra <peterz@infradead.org> > > > > 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. > > Where we are checking if VMA has changed or not since the fault ?
Not there yet, this is what you call a preparatory patch. They help review in that you can consider smaller steps.
> > diff --git a/mm/memory.c b/mm/memory.c > > index fd952f05e016..40834444ea0d 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -2240,6 +2240,12 @@ static inline void wp_page_reuse(struct vm_fault *vmf) > > pte_unmap_unlock(vmf->pte, vmf->ptl); > > } > > > > +static bool pte_map_lock(struct vm_fault *vmf) > > +{ > > + vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); > > + return true; > > +} > > This is always true ? Then we should not have all these if (!pte_map_lock(vmf)) > check blocks down below.
Later patches will make it possible to return false. This patch is about the placing this call. Having this in a separate patch makes it easier to review all those new error conditions.
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