Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper

[Vineet Gupta]

On 06/21/2017 04:27 AM, Catalin Marinas wrote:
> On Wed, Jun 21, 2017 at 12:53:03PM +0300, Kirill A. Shutemov wrote:
> > > > > > > On Thu, Jun 15, 2017 at 05:52:22PM +0300, Kirill A. Shutemov wrote:
> > > > > > > > We need an atomic way to setup pmd page table entry, avoiding races with
> > > > > > > > CPU setting dirty/accessed bits. This is required to implement
> > > > > > > > pmdp_invalidate() that doesn't loose these bits.
> [...]
> > Any chance you could help me with arm too?
> On arm (ARMv7 with LPAE) we don't have hardware updates of the
> access/dirty bits, so a generic implementation would suffice. I didn't
> find one in your patches, so here's an untested version:
>
> static inline pmd_t pmdp_establish(struct mm_struct *mm, unsigned long address,
> 				   pmd_t *pmdp, pmd_t pmd)
> {
> 	pmd_t old_pmd = *pmdp;
> 	set_pmd_at(mm, address, pmdp, pmd);
> 	return old_pmd;
> }

So it seems the discussions have settled down and pmdp_establish() can be 
implemented in generic way as above and it will suffice if arch doesn't have a 
special need. It would be nice to add the comment above generic version that it 
only needs to be implemented if hardware sets the accessed/dirty bits !

Then nothing special is needed for ARC - right ?

-Vineet