mm: set the pte dirty if the folio is already dirty

Patch series "Add folio_mk_pte()", v2.

Today if you have a folio and want to create a PTE that points to the
first page in it, you have to convert from a folio to a page.  That's
zero-cost today but will be more expensive in the future.

I didn't want to add folio_mk_pte() to each architecture, and I didn't
want to lose any optimisations that architectures have from their own
implementation of mk_pte().  Fortunately, most architectures have by now
turned their mk_pte() into a fairly bland variant of pfn_pte(), but s390
has a special optimisation that needs to be moved into generic code in the
first patch.

At the end of this patch set, we have mk_pte() and folio_mk_pte() in mm.h
and each architecture only has to implement pfn_pte().  We've also
eliminated mk_huge_pte(), mk_huge_pmd() and mk_pmd().


This patch (of 11):

If the first access to a folio is a read that is then followed by a write,
we can save a page fault.  s390 implemented this in their mk_pte() in
commit abf09bed3cce ("s390/mm: implement software dirty bits"), but other
architectures can also benefit from this.

Link: https://lkml.kernel.org/r/20250402181709.2386022-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20250402181709.2386022-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> # for s390
Cc: Zi Yan <ziy@nvidia.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Richard Weinberger <richard@nod.at>
Cc: <x86@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 3 insertions, 6 deletions

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index f8a6b54986ec..49833002232b 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1450,12 +1450,7 @@ static inline pte_t mk_pte_phys(unsigned long physpage, pgprot_t pgprot)
 
 static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
 {
-	unsigned long physpage = page_to_phys(page);
-	pte_t __pte = mk_pte_phys(physpage, pgprot);
-
-	if (pte_write(__pte) && PageDirty(page))
-		__pte = pte_mkdirty(__pte);
-	return __pte;
+	return mk_pte_phys(page_to_phys(page), pgprot);
 }
 
 #define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
diff --git a/mm/memory.c b/mm/memory.c
index 49199410805c..da4778fb3a38 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5245,6 +5245,8 @@ void set_pte_range(struct vm_fault *vmf, struct folio *folio,
 
 	if (write)
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	else if (pte_write(entry) && folio_test_dirty(folio))
+		entry = pte_mkdirty(entry);
 	if (unlikely(vmf_orig_pte_uffd_wp(vmf)))
 		entry = pte_mkuffd_wp(entry);
 	/* copy-on-write page */