Kernel Virtual Space--xkseg

Kernel Virtual Space--xkseg

When bits 63:62 are 11, access is to kernel virtual memory. Only code that is part of the kernel can access this space, a 2 TB segment starting at 0xC000 0000 0000 0000. References to this space are translated through the TLB, and cached. The kernel uses the TLB to map kernel pages in memory as required, possibly in noncontiguous locations. Although pages in kernel space are mapped, they are always associated with real memory. Kernel pages are never paged to secondary storage.

This is the space in which the IRIX kernel allocates such objects as stacks, per-process data that must be accessible on context switches, and user page tables. This area contains automatic variables declared by loadable device drivers. It is the space in which kernel-level device drivers allocate memory. Since kernel space is mapped, addresses in kseg2 that are apparently contiguous need not be contiguous in physical memory. However, a device driver can can allocate space that is both logically and physically contiguous, when that is required (see for example the kmem_alloc(D3) reference page).