Re: [RFC PATCH v2 14/27] mm: Handle THP/HugeTLB shadow stack page fault

[Yu-cheng Yu]

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,
> > Â			if (pmd_protnone(orig_pmd) &&
> > vma_is_accessible(vma))
> > Â				return do_huge_pmd_numa_page(&vmf,
> > orig_pmd);
> > Â
> > -			if (dirty && !pmd_write(orig_pmd)) {
> > +			/*
> > +			Â* Shadow stack trans huge PMDs are copy-
> > on-access,
> > +			Â* so wp_huge_pmd() on them no mater if we
> > have a
> > +			Â* write fault or not.
> > +			Â*/
> > +			if (is_shstk_mapping(vma->vm_flags) ||
> > +			ÂÂÂÂ(dirty && !pmd_write(orig_pmd))) {
> > Â				ret = wp_huge_pmd(&vmf, orig_pmd);
> > Â				if (!(ret & VM_FAULT_FALLBACK))
> > Â					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. ÂI don't know if that will create other issues.
Let me think about that.

Yu-cheng