ARM: mm: Make virt_to_pfn() a static inline

Making virt_to_pfn() a static inline taking a strongly typed
(const void *) makes the contract of a passing a pointer of that
type to the function explicit and exposes any misuse of the
macro virt_to_pfn() acting polymorphic and accepting many types
such as (void *), (unitptr_t) or (unsigned long) as arguments
without warnings.

Doing this is a bit intrusive: virt_to_pfn() requires
PHYS_PFN_OFFSET and PAGE_SHIFT to be defined, and this is defined in
<asm/page.h>, so this must be included *before* <asm/memory.h>.

The use of macros were obscuring the unclear inclusion order here,
as the macros would eventually be resolved, but a static inline
like this cannot be compiled with unresolved macros.

The naive solution to include <asm/page.h> at the top of
<asm/memory.h> does not work, because <asm/memory.h> sometimes
includes <asm/page.h> at the end of itself, which would create a
confusing inclusion loop. So instead, take the approach to always
unconditionally include <asm/page.h> at the end of <asm/memory.h>

arch/arm uses <asm/memory.h> explicitly in a lot of places,
however it turns out that if we just unconditionally include
<asm/memory.h> into <asm/page.h> and switch all inclusions of
<asm/memory.h> to <asm/page.h> instead, we enforce the right
order and <asm/memory.h> will always have access to the
definitions.

Put an inclusion guard in place making it impossible to include
<asm/memory.h> explicitly.

Link: https://lore.kernel.org/linux-mm/20220701160004.2ffff4e5ab59a55499f4c736@linux-foundation.org/
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 12 insertions, 5 deletions

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index 62e9df024445..ef2aa79ece5a 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -5,11 +5,16 @@
  *  Copyright (C) 2000-2002 Russell King
  *  modification for nommu, Hyok S. Choi, 2004
  *
- *  Note: this file should not be included by non-asm/.h files
+ *  Note: this file should not be included explicitly, include <asm/page.h>
+ *  to get access to these definitions.
  */
 #ifndef __ASM_ARM_MEMORY_H
 #define __ASM_ARM_MEMORY_H
 
+#ifndef _ASMARM_PAGE_H
+#error "Do not include <asm/memory.h> directly"
+#endif
+
 #include <linux/compiler.h>
 #include <linux/const.h>
 #include <linux/types.h>
@@ -288,10 +293,12 @@ static inline unsigned long __phys_to_virt(phys_addr_t x)
 
 #endif
 
-#define virt_to_pfn(kaddr) \
-	((((unsigned long)(kaddr) - PAGE_OFFSET) >> PAGE_SHIFT) + \
-	 PHYS_PFN_OFFSET)
-
+static inline unsigned long virt_to_pfn(const void *p)
+{
+	unsigned long kaddr = (unsigned long)p;
+	return (((kaddr - PAGE_OFFSET) >> PAGE_SHIFT) +
+		PHYS_PFN_OFFSET);
+}
 #define __pa_symbol_nodebug(x)	__virt_to_phys_nodebug((x))
 
 #ifdef CONFIG_DEBUG_VIRTUAL