arch/arm/mm/proc-macros.S - linux - Git at Google

 /*
  * We need constants.h for:
  *  VMA_VM_MM
  *  VMA_VM_FLAGS
  *  VM_EXEC
  */
 #include <asm/asm-offsets.h>
 #include <asm/thread_info.h>

 /*
  * vma_vm_mm - get mm pointer from vma pointer (vma->vm_mm)
  */
 	.macro	vma_vm_mm, rd, rn
 	ldr	\rd, [\rn, #VMA_VM_MM]
 	.endm

 /*
  * vma_vm_flags - get vma->vm_flags
  */
 	.macro	vma_vm_flags, rd, rn
 	ldr	\rd, [\rn, #VMA_VM_FLAGS]
 	.endm

 	.macro	tsk_mm, rd, rn
 	ldr	\rd, [\rn, #TI_TASK]
 	ldr	\rd, [\rd, #TSK_ACTIVE_MM]
 	.endm

 /*
  * act_mm - get current->active_mm
  */
 	.macro	act_mm, rd
 	bic	\rd, sp, #8128
 	bic	\rd, \rd, #63
 	ldr	\rd, [\rd, #TI_TASK]
 	ldr	\rd, [\rd, #TSK_ACTIVE_MM]
 	.endm

 /*
  * mmid - get context id from mm pointer (mm->context.id)
  */
 	.macro	mmid, rd, rn
 	ldr	\rd, [\rn, #MM_CONTEXT_ID]
 	.endm

 /*
  * mask_asid - mask the ASID from the context ID
  */
 	.macro	asid, rd, rn
 	and	\rd, \rn, #255
 	.endm

 	.macro	crval, clear, mmuset, ucset
 #ifdef CONFIG_MMU
 	.word	\clear
 	.word	\mmuset
 #else
 	.word	\clear
 	.word	\ucset
 #endif
 	.endm

 /*
  * dcache_line_size - get the minimum D-cache line size from the CTR register
  * on ARMv7.
  */
 	.macro	dcache_line_size, reg, tmp
 	mrc	p15, 0, \tmp, c0, c0, 1		@ read ctr
 	lsr	\tmp, \tmp, #16
 	and	\tmp, \tmp, #0xf		@ cache line size encoding
 	mov	\reg, #4			@ bytes per word
 	mov	\reg, \reg, lsl \tmp		@ actual cache line size
 	.endm

 /*
  * icache_line_size - get the minimum I-cache line size from the CTR register
  * on ARMv7.
  */
 	.macro	icache_line_size, reg, tmp
 	mrc	p15, 0, \tmp, c0, c0, 1		@ read ctr
 	and	\tmp, \tmp, #0xf		@ cache line size encoding
 	mov	\reg, #4			@ bytes per word
 	mov	\reg, \reg, lsl \tmp		@ actual cache line size
 	.endm

 /*
  * Sanity check the PTE configuration for the code below - which makes
  * certain assumptions about how these bits are laid out.
  */
 #ifdef CONFIG_MMU
 #if L_PTE_SHARED != PTE_EXT_SHARED
 #error PTE shared bit mismatch
 #endif
 #if !defined (CONFIG_ARM_LPAE) && \
 	(L_PTE_XN+L_PTE_USER+L_PTE_RDONLY+L_PTE_DIRTY+L_PTE_YOUNG+\
 	 L_PTE_FILE+L_PTE_PRESENT) > L_PTE_SHARED
 #error Invalid Linux PTE bit settings
 #endif
 #endif	/* CONFIG_MMU */

 /*
  * The ARMv6 and ARMv7 set_pte_ext translation function.
  *
  * Permission translation:
  *  YUWD  APX AP1 AP0	SVC	User
  *  0xxx   0   0   0	no acc	no acc
  *  100x   1   0   1	r/o	no acc
  *  10x0   1   0   1	r/o	no acc
  *  1011   0   0   1	r/w	no acc
  *  110x   0   1   0	r/w	r/o
  *  11x0   0   1   0	r/w	r/o
  *  1111   0   1   1	r/w	r/w
  *
  * If !CONFIG_CPU_USE_DOMAINS, the following permissions are changed:
  *  110x   1   1   1	r/o	r/o
  *  11x0   1   1   1	r/o	r/o
  */
 	.macro	armv6_mt_table pfx
 \pfx\()_mt_table:
 	.long	0x00						@ L_PTE_MT_UNCACHED
 	.long	PTE_EXT_TEX(1)					@ L_PTE_MT_BUFFERABLE
 	.long	PTE_CACHEABLE					@ L_PTE_MT_WRITETHROUGH
 	.long	PTE_CACHEABLE | PTE_BUFFERABLE			@ L_PTE_MT_WRITEBACK
 	.long	PTE_BUFFERABLE					@ L_PTE_MT_DEV_SHARED
 	.long	0x00						@ unused
 	.long	0x00						@ L_PTE_MT_MINICACHE (not present)
 	.long	PTE_EXT_TEX(1) | PTE_CACHEABLE | PTE_BUFFERABLE	@ L_PTE_MT_WRITEALLOC
 	.long	0x00						@ unused
 	.long	PTE_EXT_TEX(1)					@ L_PTE_MT_DEV_WC
 	.long	0x00						@ unused
 	.long	PTE_CACHEABLE | PTE_BUFFERABLE			@ L_PTE_MT_DEV_CACHED
 	.long	PTE_EXT_TEX(2)					@ L_PTE_MT_DEV_NONSHARED
 	.long	0x00						@ unused
 	.long	0x00						@ unused
 	.long	0x00						@ unused
 	.endm

 	.macro	armv6_set_pte_ext pfx
 	str	r1, [r0], #2048			@ linux version

 	bic	r3, r1, #0x000003fc
 	bic	r3, r3, #PTE_TYPE_MASK
 	orr	r3, r3, r2
 	orr	r3, r3, #PTE_EXT_AP0 | 2

 	adr	ip, \pfx\()_mt_table
 	and	r2, r1, #L_PTE_MT_MASK
 	ldr	r2, [ip, r2]

 	eor	r1, r1, #L_PTE_DIRTY
 	tst	r1, #L_PTE_DIRTY|L_PTE_RDONLY
 	orrne	r3, r3, #PTE_EXT_APX

 	tst	r1, #L_PTE_USER
 	orrne	r3, r3, #PTE_EXT_AP1
 #ifdef CONFIG_CPU_USE_DOMAINS
 	@ allow kernel read/write access to read-only user pages
 	tstne	r3, #PTE_EXT_APX
 	bicne	r3, r3, #PTE_EXT_APX | PTE_EXT_AP0
 #endif

 	tst	r1, #L_PTE_XN
 	orrne	r3, r3, #PTE_EXT_XN

 	orr	r3, r3, r2

 	tst	r1, #L_PTE_YOUNG
 	tstne	r1, #L_PTE_PRESENT
 	moveq	r3, #0
 #ifndef CONFIG_CPU_USE_DOMAINS
 	tstne	r1, #L_PTE_NONE
 	movne	r3, #0
 #endif

 	str	r3, [r0]
 	mcr	p15, 0, r0, c7, c10, 1		@ flush_pte
 	.endm


 /*
  * The ARMv3, ARMv4 and ARMv5 set_pte_ext translation function,
  * covering most CPUs except Xscale and Xscale 3.
  *
  * Permission translation:
  *  YUWD   AP	SVC	User
  *  0xxx  0x00	no acc	no acc
  *  100x  0x00	r/o	no acc
  *  10x0  0x00	r/o	no acc
  *  1011  0x55	r/w	no acc
  *  110x  0xaa	r/w	r/o
  *  11x0  0xaa	r/w	r/o
  *  1111  0xff	r/w	r/w
  */
 	.macro	armv3_set_pte_ext wc_disable=1
 	str	r1, [r0], #2048			@ linux version

 	eor	r3, r1, #L_PTE_PRESENT | L_PTE_YOUNG | L_PTE_DIRTY

 	bic	r2, r1, #PTE_SMALL_AP_MASK	@ keep C, B bits
 	bic	r2, r2, #PTE_TYPE_MASK
 	orr	r2, r2, #PTE_TYPE_SMALL

 	tst	r3, #L_PTE_USER			@ user?
 	orrne	r2, r2, #PTE_SMALL_AP_URO_SRW

 	tst	r3, #L_PTE_RDONLY | L_PTE_DIRTY	@ write and dirty?
 	orreq	r2, r2, #PTE_SMALL_AP_UNO_SRW

 	tst	r3, #L_PTE_PRESENT | L_PTE_YOUNG	@ present and young?
 	movne	r2, #0

 	.if	\wc_disable
 #ifdef CONFIG_CPU_DCACHE_WRITETHROUGH
 	tst	r2, #PTE_CACHEABLE
 	bicne	r2, r2, #PTE_BUFFERABLE
 #endif
 	.endif
 	str	r2, [r0]		@ hardware version
 	.endm


 /*
  * Xscale set_pte_ext translation, split into two halves to cope
  * with work-arounds.  r3 must be preserved by code between these
  * two macros.
  *
  * Permission translation:
  *  YUWD  AP	SVC	User
  *  0xxx  00	no acc	no acc
  *  100x  00	r/o	no acc
  *  10x0  00	r/o	no acc
  *  1011  01	r/w	no acc
  *  110x  10	r/w	r/o
  *  11x0  10	r/w	r/o
  *  1111  11	r/w	r/w
  */
 	.macro	xscale_set_pte_ext_prologue
 	str	r1, [r0]			@ linux version

 	eor	r3, r1, #L_PTE_PRESENT | L_PTE_YOUNG | L_PTE_DIRTY

 	bic	r2, r1, #PTE_SMALL_AP_MASK	@ keep C, B bits
 	orr	r2, r2, #PTE_TYPE_EXT		@ extended page

 	tst	r3, #L_PTE_USER			@ user?
 	orrne	r2, r2, #PTE_EXT_AP_URO_SRW	@ yes -> user r/o, system r/w

 	tst	r3, #L_PTE_RDONLY | L_PTE_DIRTY	@ write and dirty?
 	orreq	r2, r2, #PTE_EXT_AP_UNO_SRW	@ yes -> user n/a, system r/w
 						@ combined with user -> user r/w
 	.endm

 	.macro	xscale_set_pte_ext_epilogue
 	tst	r3, #L_PTE_PRESENT | L_PTE_YOUNG	@ present and young?
 	movne	r2, #0				@ no -> fault

 	str	r2, [r0, #2048]!		@ hardware version
 	mov	ip, #0
 	mcr	p15, 0, r0, c7, c10, 1		@ clean L1 D line
 	mcr	p15, 0, ip, c7, c10, 4		@ data write barrier
 	.endm

 .macro define_processor_functions name:req, dabort:req, pabort:req, nommu=0, suspend=0
 	.type	\name\()_processor_functions, #object
 	.align 2
 ENTRY(\name\()_processor_functions)
 	.word	\dabort
 	.word	\pabort
 	.word	cpu_\name\()_proc_init
 	.word	cpu_\name\()_proc_fin
 	.word	cpu_\name\()_reset
 	.word	cpu_\name\()_do_idle
 	.word	cpu_\name\()_dcache_clean_area
 	.word	cpu_\name\()_switch_mm

 	.if \nommu
 	.word	0
 	.else
 	.word	cpu_\name\()_set_pte_ext
 	.endif

 	.if \suspend
 	.word	cpu_\name\()_suspend_size
 #ifdef CONFIG_PM_SLEEP
 	.word	cpu_\name\()_do_suspend
 	.word	cpu_\name\()_do_resume
 #else
 	.word	0
 	.word	0
 #endif
 	.else
 	.word	0
 	.word	0
 	.word	0
 	.endif

 	.size	\name\()_processor_functions, . - \name\()_processor_functions
 .endm

 .macro define_cache_functions name:req
 	.align 2
 	.type	\name\()_cache_fns, #object
 ENTRY(\name\()_cache_fns)
 	.long	\name\()_flush_icache_all
 	.long	\name\()_flush_kern_cache_all
 	.long   \name\()_flush_kern_cache_louis
 	.long	\name\()_flush_user_cache_all
 	.long	\name\()_flush_user_cache_range
 	.long	\name\()_coherent_kern_range
 	.long	\name\()_coherent_user_range
 	.long	\name\()_flush_kern_dcache_area
 	.long	\name\()_dma_map_area
 	.long	\name\()_dma_unmap_area
 	.long	\name\()_dma_flush_range
 	.size	\name\()_cache_fns, . - \name\()_cache_fns
 .endm

 .macro define_tlb_functions name:req, flags_up:req, flags_smp
 	.type	\name\()_tlb_fns, #object
 ENTRY(\name\()_tlb_fns)
 	.long	\name\()_flush_user_tlb_range
 	.long	\name\()_flush_kern_tlb_range
 	.ifnb \flags_smp
 		ALT_SMP(.long	\flags_smp )
 		ALT_UP(.long	\flags_up )
 	.else
 		.long	\flags_up
 	.endif
 	.size	\name\()_tlb_fns, . - \name\()_tlb_fns
 .endm
	/*
	* We need constants.h for:
	* VMA_VM_MM
	* VMA_VM_FLAGS
	* VM_EXEC
	*/
	#include <asm/asm-offsets.h>
	#include <asm/thread_info.h>

	/*
	* vma_vm_mm - get mm pointer from vma pointer (vma->vm_mm)
	*/
	.macro vma_vm_mm, rd, rn
	ldr \rd, [\rn, #VMA_VM_MM]
	.endm

	/*
	* vma_vm_flags - get vma->vm_flags
	*/
	.macro vma_vm_flags, rd, rn
	ldr \rd, [\rn, #VMA_VM_FLAGS]
	.endm

	.macro tsk_mm, rd, rn
	ldr \rd, [\rn, #TI_TASK]
	ldr \rd, [\rd, #TSK_ACTIVE_MM]
	.endm

	/*
	* act_mm - get current->active_mm
	*/
	.macro act_mm, rd
	bic \rd, sp, #8128
	bic \rd, \rd, #63
	ldr \rd, [\rd, #TI_TASK]
	ldr \rd, [\rd, #TSK_ACTIVE_MM]
	.endm

	/*
	* mmid - get context id from mm pointer (mm->context.id)
	*/
	.macro mmid, rd, rn
	ldr \rd, [\rn, #MM_CONTEXT_ID]
	.endm

	/*
	* mask_asid - mask the ASID from the context ID
	*/
	.macro asid, rd, rn
	and \rd, \rn, #255
	.endm

	.macro crval, clear, mmuset, ucset
	#ifdef CONFIG_MMU
	.word \clear
	.word \mmuset
	#else
	.word \clear
	.word \ucset
	#endif
	.endm

	/*
	* dcache_line_size - get the minimum D-cache line size from the CTR register
	* on ARMv7.
	*/
	.macro dcache_line_size, reg, tmp
	mrc p15, 0, \tmp, c0, c0, 1 @ read ctr
	lsr \tmp, \tmp, #16
	and \tmp, \tmp, #0xf @ cache line size encoding
	mov \reg, #4 @ bytes per word
	mov \reg, \reg, lsl \tmp @ actual cache line size
	.endm

	/*
	* icache_line_size - get the minimum I-cache line size from the CTR register
	* on ARMv7.
	*/
	.macro icache_line_size, reg, tmp
	mrc p15, 0, \tmp, c0, c0, 1 @ read ctr
	and \tmp, \tmp, #0xf @ cache line size encoding
	mov \reg, #4 @ bytes per word
	mov \reg, \reg, lsl \tmp @ actual cache line size
	.endm

	/*
	* Sanity check the PTE configuration for the code below - which makes
	* certain assumptions about how these bits are laid out.
	*/
	#ifdef CONFIG_MMU
	#if L_PTE_SHARED != PTE_EXT_SHARED
	#error PTE shared bit mismatch
	#endif
	#if !defined (CONFIG_ARM_LPAE) && \
	(L_PTE_XN+L_PTE_USER+L_PTE_RDONLY+L_PTE_DIRTY+L_PTE_YOUNG+\
	L_PTE_FILE+L_PTE_PRESENT) > L_PTE_SHARED
	#error Invalid Linux PTE bit settings
	#endif
	#endif /* CONFIG_MMU */

	/*
	* The ARMv6 and ARMv7 set_pte_ext translation function.
	*
	* Permission translation:
	* YUWD APX AP1 AP0 SVC User
	* 0xxx 0 0 0 no acc no acc
	* 100x 1 0 1 r/o no acc
	* 10x0 1 0 1 r/o no acc
	* 1011 0 0 1 r/w no acc
	* 110x 0 1 0 r/w r/o
	* 11x0 0 1 0 r/w r/o
	* 1111 0 1 1 r/w r/w
	*
	* If !CONFIG_CPU_USE_DOMAINS, the following permissions are changed:
	* 110x 1 1 1 r/o r/o
	* 11x0 1 1 1 r/o r/o
	*/
	.macro armv6_mt_table pfx
	\pfx\()_mt_table:
	.long 0x00 @ L_PTE_MT_UNCACHED
	.long PTE_EXT_TEX(1) @ L_PTE_MT_BUFFERABLE
	.long PTE_CACHEABLE @ L_PTE_MT_WRITETHROUGH
	.long PTE_CACHEABLE \| PTE_BUFFERABLE @ L_PTE_MT_WRITEBACK
	.long PTE_BUFFERABLE @ L_PTE_MT_DEV_SHARED
	.long 0x00 @ unused
	.long 0x00 @ L_PTE_MT_MINICACHE (not present)
	.long PTE_EXT_TEX(1) \| PTE_CACHEABLE \| PTE_BUFFERABLE @ L_PTE_MT_WRITEALLOC
	.long 0x00 @ unused
	.long PTE_EXT_TEX(1) @ L_PTE_MT_DEV_WC
	.long 0x00 @ unused
	.long PTE_CACHEABLE \| PTE_BUFFERABLE @ L_PTE_MT_DEV_CACHED
	.long PTE_EXT_TEX(2) @ L_PTE_MT_DEV_NONSHARED
	.long 0x00 @ unused
	.long 0x00 @ unused
	.long 0x00 @ unused
	.endm

	.macro armv6_set_pte_ext pfx
	str r1, [r0], #2048 @ linux version

	bic r3, r1, #0x000003fc
	bic r3, r3, #PTE_TYPE_MASK
	orr r3, r3, r2
	orr r3, r3, #PTE_EXT_AP0 \| 2

	adr ip, \pfx\()_mt_table
	and r2, r1, #L_PTE_MT_MASK
	ldr r2, [ip, r2]

	eor r1, r1, #L_PTE_DIRTY
	tst r1, #L_PTE_DIRTY\|L_PTE_RDONLY
	orrne r3, r3, #PTE_EXT_APX

	tst r1, #L_PTE_USER
	orrne r3, r3, #PTE_EXT_AP1
	#ifdef CONFIG_CPU_USE_DOMAINS
	@ allow kernel read/write access to read-only user pages
	tstne r3, #PTE_EXT_APX
	bicne r3, r3, #PTE_EXT_APX \| PTE_EXT_AP0
	#endif

	tst r1, #L_PTE_XN
	orrne r3, r3, #PTE_EXT_XN

	orr r3, r3, r2

	tst r1, #L_PTE_YOUNG
	tstne r1, #L_PTE_PRESENT
	moveq r3, #0
	#ifndef CONFIG_CPU_USE_DOMAINS
	tstne r1, #L_PTE_NONE
	movne r3, #0
	#endif

	str r3, [r0]
	mcr p15, 0, r0, c7, c10, 1 @ flush_pte
	.endm


	/*
	* The ARMv3, ARMv4 and ARMv5 set_pte_ext translation function,
	* covering most CPUs except Xscale and Xscale 3.
	*
	* Permission translation:
	* YUWD AP SVC User
	* 0xxx 0x00 no acc no acc
	* 100x 0x00 r/o no acc
	* 10x0 0x00 r/o no acc
	* 1011 0x55 r/w no acc
	* 110x 0xaa r/w r/o
	* 11x0 0xaa r/w r/o
	* 1111 0xff r/w r/w
	*/
	.macro armv3_set_pte_ext wc_disable=1
	str r1, [r0], #2048 @ linux version

	eor r3, r1, #L_PTE_PRESENT \| L_PTE_YOUNG \| L_PTE_DIRTY

	bic r2, r1, #PTE_SMALL_AP_MASK @ keep C, B bits
	bic r2, r2, #PTE_TYPE_MASK
	orr r2, r2, #PTE_TYPE_SMALL

	tst r3, #L_PTE_USER @ user?
	orrne r2, r2, #PTE_SMALL_AP_URO_SRW

	tst r3, #L_PTE_RDONLY \| L_PTE_DIRTY @ write and dirty?
	orreq r2, r2, #PTE_SMALL_AP_UNO_SRW

	tst r3, #L_PTE_PRESENT \| L_PTE_YOUNG @ present and young?
	movne r2, #0

	.if \wc_disable
	#ifdef CONFIG_CPU_DCACHE_WRITETHROUGH
	tst r2, #PTE_CACHEABLE
	bicne r2, r2, #PTE_BUFFERABLE
	#endif
	.endif
	str r2, [r0] @ hardware version
	.endm


	/*
	* Xscale set_pte_ext translation, split into two halves to cope
	* with work-arounds. r3 must be preserved by code between these
	* two macros.
	*
	* Permission translation:
	* YUWD AP SVC User
	* 0xxx 00 no acc no acc
	* 100x 00 r/o no acc
	* 10x0 00 r/o no acc
	* 1011 01 r/w no acc
	* 110x 10 r/w r/o
	* 11x0 10 r/w r/o
	* 1111 11 r/w r/w
	*/
	.macro xscale_set_pte_ext_prologue
	str r1, [r0] @ linux version

	eor r3, r1, #L_PTE_PRESENT \| L_PTE_YOUNG \| L_PTE_DIRTY

	bic r2, r1, #PTE_SMALL_AP_MASK @ keep C, B bits
	orr r2, r2, #PTE_TYPE_EXT @ extended page

	tst r3, #L_PTE_USER @ user?
	orrne r2, r2, #PTE_EXT_AP_URO_SRW @ yes -> user r/o, system r/w

	tst r3, #L_PTE_RDONLY \| L_PTE_DIRTY @ write and dirty?
	orreq r2, r2, #PTE_EXT_AP_UNO_SRW @ yes -> user n/a, system r/w
	@ combined with user -> user r/w
	.endm

	.macro xscale_set_pte_ext_epilogue
	tst r3, #L_PTE_PRESENT \| L_PTE_YOUNG @ present and young?
	movne r2, #0 @ no -> fault

	str r2, [r0, #2048]! @ hardware version
	mov ip, #0
	mcr p15, 0, r0, c7, c10, 1 @ clean L1 D line
	mcr p15, 0, ip, c7, c10, 4 @ data write barrier
	.endm

	.macro define_processor_functions name:req, dabort:req, pabort:req, nommu=0, suspend=0
	.type \name\()_processor_functions, #object
	.align 2
	ENTRY(\name\()_processor_functions)
	.word \dabort
	.word \pabort
	.word cpu_\name\()_proc_init
	.word cpu_\name\()_proc_fin
	.word cpu_\name\()_reset
	.word cpu_\name\()_do_idle
	.word cpu_\name\()_dcache_clean_area
	.word cpu_\name\()_switch_mm

	.if \nommu
	.word 0
	.else
	.word cpu_\name\()_set_pte_ext
	.endif

	.if \suspend
	.word cpu_\name\()_suspend_size
	#ifdef CONFIG_PM_SLEEP
	.word cpu_\name\()_do_suspend
	.word cpu_\name\()_do_resume
	#else
	.word 0
	.word 0
	#endif
	.else
	.word 0
	.word 0
	.word 0
	.endif

	.size \name\()_processor_functions, . - \name\()_processor_functions
	.endm

	.macro define_cache_functions name:req
	.align 2
	.type \name\()_cache_fns, #object
	ENTRY(\name\()_cache_fns)
	.long \name\()_flush_icache_all
	.long \name\()_flush_kern_cache_all
	.long \name\()_flush_kern_cache_louis
	.long \name\()_flush_user_cache_all
	.long \name\()_flush_user_cache_range
	.long \name\()_coherent_kern_range
	.long \name\()_coherent_user_range
	.long \name\()_flush_kern_dcache_area
	.long \name\()_dma_map_area
	.long \name\()_dma_unmap_area
	.long \name\()_dma_flush_range
	.size \name\()_cache_fns, . - \name\()_cache_fns
	.endm

	.macro define_tlb_functions name:req, flags_up:req, flags_smp
	.type \name\()_tlb_fns, #object
	ENTRY(\name\()_tlb_fns)
	.long \name\()_flush_user_tlb_range
	.long \name\()_flush_kern_tlb_range
	.ifnb \flags_smp
	ALT_SMP(.long \flags_smp )
	ALT_UP(.long \flags_up )
	.else
	.long \flags_up
	.endif
	.size \name\()_tlb_fns, . - \name\()_tlb_fns
	.endm