linux-kernel - Re: [PATCH v3 10/16] mm: replace pmd_to_swp_entry() with softleaf_from

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Message-ID: <0c429a7d-cc12-49b6-bc71-4b219683743c@lucifer.local>
Date: Fri, 21 Nov 2025 19:22:41 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
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        Alexander Viro <viro@...iv.linux.org.uk>,
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Subject: Re: [PATCH v3 10/16] mm: replace pmd_to_swp_entry() with
 softleaf_from_pmd()

On Fri, Nov 21, 2025 at 07:42:50PM +0100, Vlastimil Babka wrote:
> On 11/10/25 23:21, Lorenzo Stoakes wrote:
> > Introduce softleaf_from_pmd() to do the equivalent operation for PMDs that
> > softleaf_from_pte() fulfils, and cascade changes through code base
> > accordingly, introducing helpers as necessary.
>
> Some of that is adding new pte stuff too, so it could have been separate
> patch, but it's not a big deal.

Yeah is always tricky to figure out how to separate things so tried to get
a reasonable balance :)

>
> > We are then able to eliminate pmd_to_swp_entry(), is_pmd_migration_entry(),
> > is_pmd_device_private_entry() and is_pmd_non_present_folio_entry().
> >
> > This further establishes the use of leaf operations throughout the code
> > base and further establishes the foundations for eliminating is_swap_pmd().
> >
> > No functional change intended.
> >
> > Reviewed-by: SeongJae Park <sj@...nel.org>
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Thanks!

>
> Assuming the below is fixed. Glad I could demonstrate I'm not just rubber
> stamping all this ;P
> (probably missed stuff anyway, as usual)

:)

>
> > --- a/mm/page_table_check.c
> > +++ b/mm/page_table_check.c
> > @@ -8,7 +8,7 @@
> >  #include <linux/mm.h>
> >  #include <linux/page_table_check.h>
> >  #include <linux/swap.h>
> > -#include <linux/swapops.h>
> > +#include <linux/leafops.h>
> >
> >  #undef pr_fmt
> >  #define pr_fmt(fmt)	"page_table_check: " fmt
> > @@ -179,10 +179,10 @@ void __page_table_check_pud_clear(struct mm_struct *mm, pud_t pud)
> >  EXPORT_SYMBOL(__page_table_check_pud_clear);
> >
> >  /* Whether the swap entry cached writable information */
> > -static inline bool swap_cached_writable(swp_entry_t entry)
> > +static inline bool softleaf_cached_writable(softleaf_t entry)
> >  {
> > -	return is_writable_device_private_entry(entry) ||
> > -	       is_writable_migration_entry(entry);
> > +	return softleaf_is_device_private(entry) ||
>
> Shouldn't there be softleaf_is_device_private_write(entry) ?

Ah yeah you're right. I don't think this probably matters here in practice
(as in, it'd probably be a bug if pmd_swp_uffd_wp() was true but also read
device private entry).

But it's incorrect obviously and a mistake, will send fix-patch! Thanks! :)

>
> > +		softleaf_is_migration_write(entry);
> >  }
> >
> >  static void page_table_check_pte_flags(pte_t pte)
> > @@ -190,9 +190,9 @@ static void page_table_check_pte_flags(pte_t pte)
> >  	if (pte_present(pte)) {
> >  		WARN_ON_ONCE(pte_uffd_wp(pte) && pte_write(pte));
> >  	} else if (pte_swp_uffd_wp(pte)) {
> > -		const swp_entry_t entry = pte_to_swp_entry(pte);
> > +		const softleaf_t entry = softleaf_from_pte(pte);
> >
> > -		WARN_ON_ONCE(swap_cached_writable(entry));
> > +		WARN_ON_ONCE(softleaf_cached_writable(entry));
> >  	}
> >  }
> >
> > @@ -219,9 +219,9 @@ static inline void page_table_check_pmd_flags(pmd_t pmd)
> >  		if (pmd_uffd_wp(pmd))
> >  			WARN_ON_ONCE(pmd_write(pmd));
> >  	} else if (pmd_swp_uffd_wp(pmd)) {
> > -		swp_entry_t entry = pmd_to_swp_entry(pmd);
> > +		const softleaf_t entry = softleaf_from_pmd(pmd);
> >
> > -		WARN_ON_ONCE(swap_cached_writable(entry));
> > +		WARN_ON_ONCE(softleaf_cached_writable(entry));
> >  	}
> >  }
> >