On Sat, Jun 30, 2001 at 02:51:17PM +0530, Raghav P wrote: > I was going thru the TLB exception for R2300 and had the following doubts > which I hope someone can help me out with. ( am sorry if this is a newbie > question but since this is MIPS specific I am posting here) > > The code is in arch/mips/kernel/head.S for user TLB: > > /* TLB refill, EXL == 0, R[23]00 version */ > LEAF(except_vec0_r2300) > .set noat > .set mips1 > mfc0 k0, CP0_BADVADDR > lw k1, current_pgd # get pgd pointer > srl k0, k0, 22 > sll k0, k0, 2 > addu k1, k1, k0 > mfc0 k0, CP0_CONTEXT > lw k1, (k1) > and k0, k0, 0xffc > addu k1, k1, k0 > lw k0, (k1) > nop > mtc0 k0, CP0_ENTRYLO0 > mfc0 k1, CP0_EPC > tlbwr > jr k1 > rfe > END(except_vec0_r2300) > > My linux book says that pgd and pte entries are not setup by the kernel > until a pagefault exception occurs. > The above code will work only if the pgd and pte tables are stored in kseg2; > if they were stored in kseg0 then if a pgd has an invalid pte entry the > above code will index into an invalid pte page and get a wrong physical > address. > But the pgd_alloc() and pte_alloc() routines seem to be allocating physical > pages from kseg0 for pgd and pte tables. > Am I missing something here??? We avoid having to deal with the special case of a non-existant parts of the page table except the actual ptes themselfes by having making those pgd pointers point to invalid_pte_table. Ralf
