Re: [PATCH 3/5] mm/parisc: constify ptep_get() argument

[Helge Deller <deller@kernel.org>]

* John David Anglin <dave.anglin@bell.net>:
> On 2026-07-25 12:27 p.m., Helge Deller wrote:
> > On 7/24/26 17:48, Usama Arif wrote:
> >>
> >>
> >> On 24/07/2026 16:32, Pedro Falcato wrote:
> >>> On Fri, Jul 24, 2026 at 04:03:44PM +0100, Usama Arif wrote:
> >>>>
> >>>>
> >>>> On 24/07/2026 15:14, Matthew Wilcox wrote:
> >>>>> On Fri, Jul 24, 2026 at 02:36:59PM +0100, Usama Arif wrote:
> >>>>>>
> >>>>>>
> >>>>>> On 24/07/2026 11:20, Pedro Falcato wrote:
> >>>>>>> ptep_get() does not need write access to the PTE.
> >>>>>>>
> >>>>>>> Signed-off-by: Pedro Falcato <pfalcato@suse.de>
> >>>>>>> ---
> >>>>>>>   arch/parisc/include/asm/pgtable.h | 2 +-
> >>>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>>>
> >>>>>> hmm I think you might break build bisectibility if
> >>>>>> you separate out the patches, you should squash patch 3 and 4,
> >>>>>> with patch 1.
> >>>>>
> >>>>> I don't see how this breaks bisectability.  Can you elaborate on what
> >>>>> you think would break?
> >>>>
> >>>> Patch 1 does:
> >>>>
> >>>> -static inline pte_t ptep_get_lockless(pte_t *ptep)
> >>>> +static inline pte_t ptep_get_lockless(const pte_t *ptep)
> >>>>   {
> >>>>       return ptep_get(ptep);
> >>>>   }
> >>>>
> >>>>
> >>>> ptep_get() takes a non-const arg till patch 3 for example for parsic.
> >>>> I don't think you can pass a const variable to non const function arg?
> >>>>
> >>>> So parsic won't compile in patch 1 and 2, powerprc wont compile
> >>>> for patches 1, 2 and 3..
> >>>
> >>> Aha, yes, nice catch! I'll have to rethink that. Maybe squashing the patches
> >>> would be the cleanest way forward.
> >>>
> >>
> >> Yes, squashing is the simplest way forward.
> >>
> >>> FWIW, the vast majority of architectures aren't doing funny things on
> >>> ptep_get(). E.g PA-RISC, loongarch only define these so they can use it in
> >>> their own asm/pgtable.h. I'd really like to delete these but I can't tell
> >>> if they are *actually* required.
> >>>
> >>
> >> Ah maybe there is something in git history on why it was needed?
> >>
> >> If not, hopefully someone from the arch lists could clarify..
> > I tried to remove ptep_get() and ptep_test_and_clear_young() from
> > arch/parisc/include/asm/pgtable.h, but this then triggers compile errors:
> > 
> >  CC      arch/parisc/kernel/asm-offsets.s
> > In file included from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/mm.h:31,
> >                  from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/pid_namespace.h:7,
> >                  from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/ptrace.h:10,
> >                  from /home/cvs/parisc/git-kernel/linus-linux-2.6/arch/parisc/kernel/asm-offsets.c:21:
> > /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/pgtable.h: In function ‘clear_young_dirty_ptes’:
> > /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/pgtable.h:683:25: error: implicit declaration of function ‘ptep_test_and_clear_young’;
> > did you mean ‘pmdp_test_and_clear_young’? [-Wimplicit-function-declaration]
> >   683 |                         ptep_test_and_clear_young(vma, addr, ptep);
> >       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~
> >       |                         pmdp_test_and_clear_young
> > 
> > So, I think the answer is, that the local copy of ptep_get() is used in the parisc implementation of
> > ptep_test_and_clear_young() function.
> > 
> > Switching to the default include/linux/pgtable.h seems not easy doable....
> 
> Did you remove define for __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG in parisc version of pgtable.h?

Indeed, I missed to remove that.

Usama, if you want you can add the patch below to your patch set, thus
simplifying your series?

Helge

------

From: Helge Deller <deller@gmx.de>
Date: Sat, 25 Jul 2026 19:19:55 +0200
Subject: [PATCH] parisc: Drop own implementations for ptep_get() and
 ptep_test_and_clear_young()

Switch to the generic implementations, which are identical.

Suggested-by: Usama Arif <usama.arif@linux.dev>
Suggested-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/include/asm/pgtable.h b/arch/parisc/include/asm/pgtable.h
index 467b8547ac8b..d92dee9fef3f 100644
--- a/arch/parisc/include/asm/pgtable.h
+++ b/arch/parisc/include/asm/pgtable.h
@@ -432,25 +432,6 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
 	return pte;
 }
 
-static inline pte_t ptep_get(pte_t *ptep)
-{
-	return READ_ONCE(*ptep);
-}
-#define ptep_get ptep_get
-
-static inline bool ptep_test_and_clear_young(struct vm_area_struct *vma,
-		unsigned long addr, pte_t *ptep)
-{
-	pte_t pte;
-
-	pte = ptep_get(ptep);
-	if (!pte_young(pte)) {
-		return false;
-	}
-	set_pte_at(vma->vm_mm, addr, ptep, pte_mkold(pte));
-	return true;
-}
-
 bool ptep_clear_flush_young(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep);
 pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep);
 
@@ -491,7 +472,6 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
 #define HAVE_ARCH_UNMAPPED_AREA
 #define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
 
-#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
 #define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
 #define __HAVE_ARCH_PTEP_CLEAR_FLUSH
 #define __HAVE_ARCH_PTEP_SET_WRPROTECT