Memory Management Unit

Collaboration diagram for Memory Management Unit:

Modules
	MMU - X86 specific

Enumerations
enum	mmu_prot {   PROT_NONE = 0x0 , PROT_EXEC = 0x1 , PROT_READ = 0x2 , PROT_WRITE = 0x4 ,   PROT_KERNEL = 0x8 }
	Protection flags passed to the mmu's functions. More...

Functions
bool	mmu_init (void)
	Initialize the MMU's paging system. More...
paddr_t	mmu_new (void)
	Allocate and initialize a new page directory. More...
void	mmu_destroy (paddr_t mmu)
	Release the MMU's page_directory. More...
void	mmu_clone (paddr_t destination)
	Clone the current MMU inside another one.
error_t	mmu_copy_on_write (vaddr_t)
	Try to remap a potential copy-on-write mapping.
void	mmu_load (paddr_t mmu)
	Replace the current page directory. More...
bool	mmu_map (vaddr_t virt, paddr_t physical, int prot)
	Map a virtual address to a physical one. More...
bool	mmu_map_range (vaddr_t virt, paddr_t physical, size_t size, int prot)
	Map a range of virtual addresses to physical ones. More...
paddr_t	mmu_unmap (vaddr_t virt)
	Unmap a virtual address. More...
void	mmu_unmap_range (vaddr_t start, vaddr_t end)
	Unmap a range of virtual addresses. More...
void	mmu_identity_map (paddr_t start, paddr_t end, int prot)
	Perform identity mapping inside a given virtual address range. More...
paddr_t	mmu_find_physical (vaddr_t)
	Find the physical mapping of a virtual address. More...
static bool	mmu_is_mapped (vaddr_t addr)

Detailed Description

Memory Managerment Unit (MMU)

Interface with the CPU's hardware MMU.

The MMU automatically translates virtual addresses into physical ones. These physical addresses should be pages, allocated using the PMM. This whole translation process is called paging.

This includes:

• Enabling/Disabling paging
• Updating the underlying structures

TODO: It should ideally be possible to modify the content of another MMU. We have no efficient way of accessing an arbitrary physical address without having to go through the VMM to find an address.

Enumeration Type Documentation

mmu_prot

enum mmu_prot

Enumerator
PROT_NONE	Pages may not be accessed
PROT_EXEC	Pages may be executed
PROT_READ	Pages may be read
PROT_WRITE	Pages may be written
PROT_KERNEL	Pages should be accessible only from the kernel

Function Documentation

mmu_destroy()

void mmu_destroy

(

paddr_t

mmu

)

Note

This function does not release all the memory that was potentially mapped by the MMU. This should be done separately by the caller.

mmu_find_physical()

paddr_t mmu_find_physical

(

vaddr_t

virtual

)

Returns

-E_INVAL if error, a physical address if none

mmu_identity_map()

void mmu_identity_map	(	paddr_t	start,
		paddr_t	end,
		int	prot
	)

Identity mapping is the process of mapping a virtual address to the same physical address.

Both start and end addresses will be included inside the range.

Parameters

start	the starting page of the address range
end	the ending address of the address range
prot	Protection rule in use for this page. A combination of mmu_prot flags.

mmu_init()

bool mmu_init

(

void

)

This function is responsible for setting any required bit inside the CPU's register.

It is also responsible of remapping the kernel's code and addresses before enabling paging.

Warning

After calling this function, each and every address will automatically be translated into its physical equivalent using the paging mechanism. Be sure to remap known addresses to avoid raising exceptions.

mmu_is_mapped()

static bool mmu_is_mapped ( vaddr_t  addr )

inlinestatic

Returns

Whether the current MMU contains a mapping for a virtual address.

mmu_load()

void mmu_load

(

paddr_t

mmu

)

Parameters

page_directory

The physical address of the page directory

mmu_map()

bool mmu_map	(	vaddr_t	virt,
		paddr_t	physical,
		int	prot
	)

Parameters

virt	The virtual address
physical	Its physical equivalent
prot	Protection rule in use for this page. A combination of mmu_prot flags.

Returns

False if the address was already mapped before

mmu_map_range()

bool mmu_map_range	(	vaddr_t	virt,
		paddr_t	physical,
		size_t	size,
		int	prot
	)

Parameters

virt	The start of the virtual address range
physical	Its physical equivalent
size	The size of the region to map
prot	Protection rule in use for this page. A combination of mmu_prot flags.

Returns

False if the address was already mapped before

mmu_new()

paddr_t mmu_new

(

void

)

Returns

The physical address of the new page_directory, 0 if error.

Allocate and initialize a new page directory.

Returns

The physical address of the new page_directory, 0 if error.

mmu_unmap()

paddr_t mmu_unmap

(

vaddr_t

virt

)

Warning

After calling this, referencing the given virtual address may cause the CPU to raise an exception.

Parameters

virt	The virtual address

Returns

The physical pageframe associated with the unmapped address

mmu_unmap_range()

void mmu_unmap_range	(	vaddr_t	start,
		vaddr_t	end
	)

Parameters

start	The start of the virtual address
end	The end of the virtual address