un

The un union is where processor-specific system page information is kept. The purpose of the union is to serve as a demultiplexing point for the various CPU families. It is demultiplexed based on the value of the type member of the system page structure.

Currently supported CPU architectures include:

un.x86 and un.x86_64

These structures contain x86-specific information. Usually, startup library functions automatically fill in the information carried in these structure:

smpinfo

Contains info on how to manipulate the SMP control hardware; filled in by the library call init_smp().

gdt

Contains the Global Descriptor Table (GDT); filled in by the library.

idt

Contains the Interrupt Descriptor Table (IDT); filled in by the library.

pgdir

Contains pointers to the Page Directory Table(s); filled in by the library.

real_addr

The virtual address corresponding to the physical address range 0 through 0xFFFFF inclusive (the bottom 1 megabyte).

un.arm and un.aarch64

These structures contain ARM-specific information. Usually, startup library functions automatically fill in the information carried in these structure:

L1_vaddr

Virtual address of the MMU level 1 page table used to map the kernel.

L1_paddr

Physical address of the MMU level 1 page table used to map the kernel.

startup_base

Virtual address of a 1-1 virtual-physical mapping used to map the startup code that enables the MMU. This virtual mapping is removed when the kernel is initialized.

startup_size

Size of the mapping used for startup_base.

cpu

Structure containing ARM core-specific operations and data (see “ARM cpu” below).

ARM cpu

Currently the ARM cpu structure contains the following routines:

page_flush

Implements CPU-specific cache/TLB flushing when the memory manager unmaps or changes the access protections to a virtual memory mapping for a page. This routine is called for each page in a range being modified by the virtual memory manager.

page_flush_deferred

Performs any operations that can be deferred when the page_flush() kernel callout is used. For example on the SA-1110 processor, an Icache flush is deferred until all pages being operated on have been modified.