PMM

Physical Memory Manager. More...

Collaboration diagram for PMM:

Macros
#define	PAGE_SIZE   4096
	4KB pages
#define	PAGE_SHIFT   12
	bits to shift to get page (2^12=4096)
#define	MEMORY_SIZE   0x100000000
	4GB address space
#define	TYPE_BITS   2
	number of bits per page entry
#define	PAGE_NUMBER   (MEMORY_SIZE / PAGE_SIZE)
	total number of pages
#define	ENTRIES   1024
	number of entries in a page table
#define	PAGES_PER_DWORD   (32 / TYPE_BITS)
	pages in each bitmap entry
#define	PAGES_BER_BYTE   (8 / TYPE_BITS)
	pages per bitmap entry byte
#define	TYPE_MASK   (0xFFFFFFFF >> (32 - TYPE_BITS))
	calc 2^TYPE_BITS-1
#define	BITMAP_INIT   0x55555555
	0b0101...01, use PMM_RESERVED
#define	BIT_CHECK(val, bit)   (((val) >> (bit)) & 1)
	checks a bit in a given value
#define	BITMAP_SET(idx)    (bitmap[(idx) / 32] |= 1 << ((idx) % 32))
	sets a bit in the memory bitmap
#define	BITMAP_CLEAR(idx)    (bitmap[(idx) / 32] &= ~(1 << ((idx) % 32)))
	clears a bit in the memory bitmap

Enumerations
enum	pmm_flags_t { PMM_UNUSED, PMM_RESERVED, PMM_KERNEL, PMM_USER }
	information on who uses a page frame (needs to fit in TYPE_BITS)

Functions
static void	pmm_bitmap_set (uint32_t idx, uint32_t value)
	Sets a bitmap entry to a value. More...
static uint32_t	pmm_bitmap_get (uint32_t idx)
	Returns a bitmap entry. More...
static void	pmm_use_kernel_memory ()
	Marks all kernel memory as used.
void	pmm_init ()
	Initializes the PMM. More...
uint32_t	pmm_get_page (void *ptr, uint32_t offset)
	Returns to which page a given memory address belongs. More...
void *	pmm_get_address (uint32_t page, uint32_t offset)
	Returns a memory address belonging to a given page. More...
void	pmm_use (void *ptr, size_t len, pmm_flags_t flags, char *tag)
	Marks page frames for a given memory range as used or unused. More...
static void *	pmm_find_free (size_t len)
	Finds free page frames. More...
void *	pmm_alloc (size_t len, pmm_flags_t flags)
	Allocates page frames. More...
void	pmm_free (void *ptr, size_t len)
	Frees page frames. More...
pmm_flags_t	pmm_check (void *ptr)
	Returns whether a page frame is used or unused. More...
void	pmm_dump (void *ptr, size_t len)
	Dumps information on page frames for a given memory range. More...
uint32_t	pmm_get_highest_kernel_page ()
	Returns the highest page used by the kernel. More...

Variables
static uint32_t	bitmap [PAGE_NUMBER/PAGES_PER_DWORD]
	Holds information on used page frames. More...
static uint32_t	highest_kernel_page = 0
	remember the highest kernel page
const void	kernel_start
	start of the kernel section
const void	kernel_end
	end of the kernel section
const void	main_kernel_stack_end
	end of the main kernel stack
static void *	main_kernel_stack_start
	start of the main kernel stack More...

Detailed Description

Physical Memory Manager.

The PMM allocates and frees physical page frames (blocks of 4KiB). It obtains an initial memory map from GRUB.

See also

http://wiki.osdev.org/Memory_management

http://wiki.osdev.org/Page_Frame_Allocation

http://www.lowlevel.eu/wiki/Physische_Speicherverwaltung

http://wiki.osdev.org/Detecting_Memory_(x86)

Function Documentation

void * pmm_alloc	(	size_t	len,
		pmm_flags_t	flags
	)

Allocates page frames.

Parameters

len	requested number of consecutive free bytes
flags	whether to allocate for kernel or user space

Returns

the physical start address of the allocated memory range

Definition at line 183 of file pmm.c.

Here is the call graph for this function:

Here is the caller graph for this function:

static uint32_t pmm_bitmap_get ( uint32_t  idx )

static

Returns a bitmap entry.

Parameters

idx	index into the bitmap

Returns

value of the bitmap entry, can be 9 to TYPE_MASK

Definition at line 72 of file pmm.c.

Here is the caller graph for this function:

static void pmm_bitmap_set ( uint32_t  idx, uint32_t  value  )

static

Sets a bitmap entry to a value.

Parameters

idx	index into the bitmap
value	value to set the entry to, can be 0 to TYPE_MASK

Definition at line 58 of file pmm.c.

Here is the caller graph for this function:

pmm_flags_t pmm_check

(

void *

ptr

)

Returns whether a page frame is used or unused.

Parameters

ptr	the physical address of the page frame to check

Returns

information on who uses the page

Definition at line 206 of file pmm.c.

Here is the call graph for this function:

Here is the caller graph for this function:

void pmm_dump	(	void *	ptr,
		size_t	len
	)

Dumps information on page frames for a given memory range.

The dump is logged.

Parameters

ptr	the physical start address of the memory range
len	the length of the memory range in bytes

Definition at line 215 of file pmm.c.

Here is the call graph for this function:

static void* pmm_find_free ( size_t  len )

static

Finds free page frames.

Parameters

len	requested number of consecutive free bytes

Returns

the physical address of a suitable free memory range

Definition at line 160 of file pmm.c.

Here is the call graph for this function:

Here is the caller graph for this function:

void pmm_free	(	void *	ptr,
		size_t	len
	)

Frees page frames.

Parameters

ptr	the physical start address of the memory range
len	the length of the memory range in bytes

Definition at line 196 of file pmm.c.

Here is the call graph for this function:

Here is the caller graph for this function:

void * pmm_get_address	(	uint32_t	page,
		uint32_t	offset
	)

Returns a memory address belonging to a given page.

Parameters

page	a page index
offset	number of bytes to add to the start of the page

Returns

the first address of the page (if given, the offset is added)

Definition at line 130 of file pmm.c.

Here is the caller graph for this function:

uint32_t pmm_get_highest_kernel_page

(

)

Returns the highest page used by the kernel.

Returns

highest kernel page

Definition at line 235 of file pmm.c.

Here is the caller graph for this function:

uint32_t pmm_get_page	(	void *	ptr,
		uint32_t	offset
	)

Returns to which page a given memory address belongs.

Parameters

ptr	a physical or virtual address
offset	number of bytes to add to ptr

Returns

the page index that contains the address ptr

Definition at line 120 of file pmm.c.

Here is the caller graph for this function:

void pmm_init

(

)

Initializes the PMM.

First assumes the whole memory is used, GRUB tells us about free memory.

Prevents that we allocate or dereference the null pointer or BIOS data by pmm_use()'ing the first page table.

Copies the multiboot structures somewhere into the kernel so we can overwrite lower memory in VM86 mode later. Because our kernel starts at 4 MiB (the 2nd page table) we reserved the first page table above so that the multiboot structures lie directly after the kernel.

After the structures were copied from lower memory, frees 0x100000-0x3FFFFF to not waste too much memory.

Definition at line 87 of file pmm.c.

Here is the call graph for this function:

void pmm_use	(	void *	ptr,
		size_t	len,
		pmm_flags_t	flags,
		char *	tag
	)

Marks page frames for a given memory range as used or unused.

Parameters

ptr	the physical start address of the memory range
len	the length of the memory range in bytes
flags	whether to allocate or free page frames
tag	a short string for the debug log

Definition at line 141 of file pmm.c.

Here is the call graph for this function:

Here is the caller graph for this function:

Variable Documentation

uint32_t bitmap[PAGE_NUMBER/PAGES_PER_DWORD]

static

Holds information on used page frames.

We could save some space here with dynamic allocation if we had it. This way we use up 2MiB of memory.

Definition at line 40 of file pmm.c.

void* main_kernel_stack_start

static

Initial value:

= (void*) ((uintptr_t)
        &main_kernel_stack_end - STACK_SIZE + 1)

start of the main kernel stack

Definition at line 50 of file pmm.c.