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

From: Vineet Gupta
Date: Wed Jun 21 2017 - 13:21:28 EST

On 06/21/2017 10:16 AM, Kirill A. Shutemov wrote:
On Wed, Jun 21, 2017 at 08:49:03AM -0700, Vineet Gupta wrote:
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 ?
I will define generic version as Catalin proposed with a comment, but
under the name generic_pmdp_establish. An arch can make use of it by

#define pmdp_establish generic_pmdp_establish

Can you do that for ARC in your next posting - or want me to once you have posted that ?

I don't want it to be used by default without attention from architecture
maintainer. It can lead unnoticied breakage if THP got enabled on new

Makes sense !