x86_round_page
endpa = x86_round_page(addr + len);
start = x86_round_page(avail_end + 1);
endpa = x86_round_page(bpa + size);
endva = x86_round_page(bsh + size);
endva = x86_round_page(bsh + size);
paddr_t endpa = x86_round_page(pa + len);