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SubjectRe: [RFC PATCH v2 14/27] mm: Handle THP/HugeTLB shadow stack page fault
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On Wed, 2018-07-11 at 11:10 +0200, Peter Zijlstra wrote:
> On Tue, Jul 10, 2018 at 03:26:26PM -0700, Yu-cheng Yu wrote:
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index a2695dbc0418..f7c46d61eaea 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -4108,7 +4108,13 @@ static int __handle_mm_fault(struct
> > vm_area_struct *vma, unsigned long address,
> >   if (pmd_protnone(orig_pmd) &&
> > vma_is_accessible(vma))
> >   return do_huge_pmd_numa_page(&vmf,
> > orig_pmd);
> >  
> > - if (dirty && !pmd_write(orig_pmd)) {
> > + /*
> > +  * Shadow stack trans huge PMDs are copy-
> > on-access,
> > +  * so wp_huge_pmd() on them no mater if we
> > have a
> > +  * write fault or not.
> > +  */
> > + if (is_shstk_mapping(vma->vm_flags) ||
> > +     (dirty && !pmd_write(orig_pmd))) {
> >   ret = wp_huge_pmd(&vmf, orig_pmd);
> >   if (!(ret & VM_FAULT_FALLBACK))
> >   return ret;
> Can't we do this (and the do_wp_page thing) by setting
> FAULT_FLAG_WRITE
> in the arch fault handler on shadow stack faults?

This can work.  I don't know if that will create other issues.
Let me think about that.

Yu-cheng
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