Merge branch 'strict-mm-typechecks-support' into features

Heiko writes:

"The recent large kernel Rust thread where Linus commented about that
structures may be returned in registers [1] made me again aware that this
is not true for s390 where the ABI defines that structures are returned in
a return value buffer allocated by the caller. This was also mentioned by
Alexander Gordeev a couple of weeks ago.

In theory the -freg-struct-return compiler flag would allow to return small
structures in registers, however that has not been implemented for
s390. Juergen Christ did an experimental gcc implementation which shows the
benefit of such a change (bloat-o-meter):

add/remove: 3/2 grow/shrink: 12/441 up/down: 740/-7182 (-6442)

This result is not very impressive, and doesn't seem to justify a new ABI
for the kernel.

However there is still the existing STRICT_MM_TYPECHECKS which can be used
to change some mm types from structures to simple scalar types. Changing
the mm types results in:

add/remove: 2/8 grow/shrink: 25/116 up/down: 3902/-6204 (-2302)

Which is already a third of the possible savings which would be the result
of the described ABI change.

Therefore add support for a configurable STRICT_MM_TYPECHECKS which allows
to generate better code, but also allows to have type checking for debug
builds."

[1] https://lore.kernel.org/all/CAHk-=wgb1g9VVHRaAnJjrfRFWAOVT2ouNOMqt0js8h3D6zvHDw@mail.gmail.com/

* strict-mm-typechecks-support:
  s390/mm: Add configurable STRICT_MM_TYPECHECKS
  s390/mm: Convert pgste_val() into function
  s390/mm: Convert pgprot_val() into function
  s390/mm: Use pgprot_val() instead of open coding

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 33 insertions, 26 deletions

diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
index 1ff145f7b52b..4e5dbabdf202 100644
--- a/arch/s390/include/asm/page.h
+++ b/arch/s390/include/asm/page.h
@@ -71,9 +71,11 @@ static inline void copy_page(void *to, void *from)
 #define vma_alloc_zeroed_movable_folio(vma, vaddr) \
 	vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
 
-/*
- * These are used to make use of C type-checking..
- */
+#ifdef CONFIG_STRICT_MM_TYPECHECKS
+#define STRICT_MM_TYPECHECKS
+#endif
+
+#ifdef STRICT_MM_TYPECHECKS
 
 typedef struct { unsigned long pgprot; } pgprot_t;
 typedef struct { unsigned long pgste; } pgste_t;
@@ -82,43 +84,48 @@ typedef struct { unsigned long pmd; } pmd_t;
 typedef struct { unsigned long pud; } pud_t;
 typedef struct { unsigned long p4d; } p4d_t;
 typedef struct { unsigned long pgd; } pgd_t;
-typedef pte_t *pgtable_t;
 
-#define pgprot_val(x)	((x).pgprot)
-#define pgste_val(x)	((x).pgste)
-
-static inline unsigned long pte_val(pte_t pte)
-{
-	return pte.pte;
+#define DEFINE_PGVAL_FUNC(name)						\
+static __always_inline unsigned long name ## _val(name ## _t name)	\
+{									\
+	return name.name;						\
 }
 
-static inline unsigned long pmd_val(pmd_t pmd)
-{
-	return pmd.pmd;
-}
+#else /* STRICT_MM_TYPECHECKS */
 
-static inline unsigned long pud_val(pud_t pud)
-{
-	return pud.pud;
-}
+typedef unsigned long pgprot_t;
+typedef unsigned long pgste_t;
+typedef unsigned long pte_t;
+typedef unsigned long pmd_t;
+typedef unsigned long pud_t;
+typedef unsigned long p4d_t;
+typedef unsigned long pgd_t;
 
-static inline unsigned long p4d_val(p4d_t p4d)
-{
-	return p4d.p4d;
+#define DEFINE_PGVAL_FUNC(name)						\
+static __always_inline unsigned long name ## _val(name ## _t name)	\
+{									\
+	return name;							\
 }
 
-static inline unsigned long pgd_val(pgd_t pgd)
-{
-	return pgd.pgd;
-}
+#endif /* STRICT_MM_TYPECHECKS */
+
+DEFINE_PGVAL_FUNC(pgprot)
+DEFINE_PGVAL_FUNC(pgste)
+DEFINE_PGVAL_FUNC(pte)
+DEFINE_PGVAL_FUNC(pmd)
+DEFINE_PGVAL_FUNC(pud)
+DEFINE_PGVAL_FUNC(p4d)
+DEFINE_PGVAL_FUNC(pgd)
+
+typedef pte_t *pgtable_t;
 
+#define __pgprot(x)	((pgprot_t) { (x) } )
 #define __pgste(x)	((pgste_t) { (x) } )
 #define __pte(x)        ((pte_t) { (x) } )
 #define __pmd(x)        ((pmd_t) { (x) } )
 #define __pud(x)	((pud_t) { (x) } )
 #define __p4d(x)	((p4d_t) { (x) } )
 #define __pgd(x)        ((pgd_t) { (x) } )
-#define __pgprot(x)     ((pgprot_t) { (x) } )
 
 static inline void page_set_storage_key(unsigned long addr,
 					unsigned char skey, int mapped)