lib/ioremap.c: add huge I/O map capability interfaces

Add ioremap_pud_enabled() and ioremap_pmd_enabled(), which return 1 when
I/O mappings with pud/pmd are enabled on the kernel.

ioremap_huge_init() calls arch_ioremap_pud_supported() and
arch_ioremap_pmd_supported() to initialize the capabilities at boot-time.

A new kernel option "nohugeiomap" is also added, so that user can disable
the huge I/O map capabilities when necessary.

Signed-off-by: Toshi Kani <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: Robert Elliott <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/kernel-parameters.txt

···
 			register save and restore. The kernel will only save
 			legacy floating-point registers on task switch.
 
+	nohugeiomap	[KNL,x86] Disable kernel huge I/O mappings.
+
 	noxsave		[BUGS=X86] Disables x86 extended register state save
 			and restore using xsave. The kernel will fallback to
 			enabling legacy floating-point and sse state.

arch/Kconfig

···
 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	bool
 
+config HAVE_ARCH_HUGE_VMAP
+	bool
+
 config HAVE_ARCH_SOFT_DIRTY
 	bool
 

include/linux/io.h

···
 }
 #endif
 
+#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
+void __init ioremap_huge_init(void);
+int arch_ioremap_pud_supported(void);
+int arch_ioremap_pmd_supported(void);
+#else
+static inline void ioremap_huge_init(void) { }
+#endif
+
 /*
  * Managed iomap interface
  */

init/main.c

···
 #include <linux/list.h>
 #include <linux/integrity.h>
 #include <linux/proc_ns.h>
+#include <linux/io.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
···
 	percpu_init_late();
 	pgtable_init();
 	vmalloc_init();
+	ioremap_huge_init();
 }
 
 asmlinkage __visible void __init start_kernel(void)

lib/ioremap.c

···
 #include <asm/cacheflush.h>
 #include <asm/pgtable.h>
 
+#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
+int __read_mostly ioremap_pud_capable;
+int __read_mostly ioremap_pmd_capable;
+int __read_mostly ioremap_huge_disabled;
+
+static int __init set_nohugeiomap(char *str)
+{
+	ioremap_huge_disabled = 1;
+	return 0;
+}
+early_param("nohugeiomap", set_nohugeiomap);
+
+void __init ioremap_huge_init(void)
+{
+	if (!ioremap_huge_disabled) {
+		if (arch_ioremap_pud_supported())
+			ioremap_pud_capable = 1;
+		if (arch_ioremap_pmd_supported())
+			ioremap_pmd_capable = 1;
+	}
+}
+
+static inline int ioremap_pud_enabled(void)
+{
+	return ioremap_pud_capable;
+}
+
+static inline int ioremap_pmd_enabled(void)
+{
+	return ioremap_pmd_capable;
+}
+
+#else	/* !CONFIG_HAVE_ARCH_HUGE_VMAP */
+static inline int ioremap_pud_enabled(void) { return 0; }
+static inline int ioremap_pmd_enabled(void) { return 0; }
+#endif	/* CONFIG_HAVE_ARCH_HUGE_VMAP */
+
 static int ioremap_pte_range(pmd_t *pmd, unsigned long addr,
 		unsigned long end, phys_addr_t phys_addr, pgprot_t prot)
 {