Zero page

[Masao Uebayashi <uebayasi%tombi.co.jp@localhost>]

I need to add zero-page to support XIP.  Unallocated blocks are redirected
to this.  Basically it's a static simgle page filled with zero.

        void *pmap_zeropage;
        paddr_t pmap_zeropage_phys_addr;

and initialized by pmap.c like:

        pmap_zeropage = (void *)uvm_pageboot_alloc(PAGE_SIZE);
        pmap_zeropage_phys_addr = MIPS_KSEG0_TO_PHYS(pmap_zeropage);

Because it's used publically (from the coming custome genfs_getpages()), it's
defined somewhere like uvm_page.h.

Masao

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Masao Uebayashi / Tombi Inc. / Tel: +81-90-9141-4635