wueddie

kernel memory mapping summay

Today, finally I become clear about the relationship between
fixed mapping
permanent kernel mapping
temporary kernel mapping
noncontiguous memory area mapping
(I feel that most of the name is not appropriate, to some text, it will mislead the reader.)

4G linear virtual address space is divided into two major part.
kernel space mapping     [3G, 4G)
user space mapping        [0, 3G)

kernel space mapping is divided into more pieces
linear mapping [3G, 3G + 896M)
non linear mapping [3G + 896M + 8M, 4G)
1. Fixed Mapping (wrong name, should be compile time mapping, the virtual address is decided in compile time. )
2. Temporary mapping
3. Permanent mapping
4. noncontiguous memory area mapping (Vmalloc area)

The following is the diagram for the reference.

FIXADDR_TOP            (=0xfffff000)
 
                    fixed_addresses (temporary kernel mapping is part of it)
                     #define __FIXADDR_SIZE  (__end_of_permanent_fixed_addresses << PAGE_SHIFT)
                
FIXADDR_START        (FIXADDR_TOP - __FIXADDR_SIZE)
                        
                    temp fixed addresses (used in boot time)
                     #define __FIXADDR_BOOT_SIZE     (__end_of_fixed_addresses << PAGE_SHIFT)
                
FIXADDR_BOOT_START    (FIXADDR_TOP - __FIXADDR_BOOT_SIZE)
                        
                    Persistent kmap area (4M)
 
PKMAP_BASE            ( (FIXADDR_BOOT_START - PAGE_SIZE*(LAST_PKMAP + 1)) & PMD_MASK )
 
                     2*PAGE_SIZE
 
VMALLOC_END            (PKMAP_BASE-2*PAGE_SIZE) or (FIXADDR_START-2*PAGE_SIZE)

                     noncontiguous memory area mapping (Vmalloc area)
                    
VMALLOC_START        (((unsigned long) high_memory + 2*VMALLOC_OFFSET-1) & ~(VMALLOC_OFFSET-1)) 

high_memory            MIN (896M, phisical memory size)
 
below the excerp of the source code.

#ifdef CONFIG_X86_PAE
#define LAST_PKMAP 512
#else
#define LAST_PKMAP 1024
#endif
                                                                         
#define VMALLOC_OFFSET  (8*1024*1024)
#define VMALLOC_START   (((unsigned long) high_memory + \                         
                        2*VMALLOC_OFFSET-1) & ~(VMALLOC_OFFSET-1))   
                              
#ifdef CONFIG_HIGHMEM                                             
# define VMALLOC_END    (PKMAP_BASE-2*PAGE_SIZE)
#else                                                                    
# define VMALLOC_END    (FIXADDR_START-2*PAGE_SIZE)              
#endif

enum fixed_addresses {
        FIX_HOLE,
        FIX_VDSO,
        FIX_DBGP_BASE,
        FIX_EARLYCON_MEM_BASE,
#ifdef CONFIG_X86_LOCAL_APIC
        FIX_APIC_BASE,  /* local (CPU) APIC) -- required for SMP or not */
#endif
#ifdef CONFIG_X86_IO_APIC
        FIX_IO_APIC_BASE_0,
        FIX_IO_APIC_BASE_END = FIX_IO_APIC_BASE_0 + MAX_IO_APICS-1,
#endif
#ifdef CONFIG_X86_VISWS_APIC
        FIX_CO_CPU,     /* Cobalt timer */
        FIX_CO_APIC,    /* Cobalt APIC Redirection Table */
        FIX_LI_PCIA,    /* Lithium PCI Bridge A */
        FIX_LI_PCIB,    /* Lithium PCI Bridge B */
#endif
#ifdef CONFIG_X86_F00F_BUG
        FIX_F00F_IDT,   /* Virtual mapping for IDT */
#endif
#ifdef CONFIG_X86_CYCLONE_TIMER
        FIX_CYCLONE_TIMER, /*cyclone timer register*/
#endif
#ifdef CONFIG_HIGHMEM
        FIX_KMAP_BEGIN, /* reserved pte's for temporary kernel mappings */
        FIX_KMAP_END = FIX_KMAP_BEGIN+(KM_TYPE_NR*NR_CPUS)-1,
#endif
#ifdef CONFIG_ACPI
        FIX_ACPI_BEGIN,
        FIX_ACPI_END = FIX_ACPI_BEGIN + FIX_ACPI_PAGES - 1,
#endif
#ifdef CONFIG_PCI_MMCONFIG
        FIX_PCIE_MCFG,
#endif
#ifdef CONFIG_PARAVIRT
        FIX_PARAVIRT_BOOTMAP,
#endif
        __end_of_permanent_fixed_addresses,
        /* temporary boot-time mappings, used before ioremap() is functional */
#define NR_FIX_BTMAPS   16
        FIX_BTMAP_END = __end_of_permanent_fixed_addresses,
        FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS - 1,
        FIX_WP_TEST,
        __end_of_fixed_addresses
}