From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: get_pteptr mystery From: Hollis Blanchard To: devel list In-Reply-To: <1040256384.30597.70.camel@granite.austin.ibm.com> References: <1040256384.30597.70.camel@granite.austin.ibm.com> Content-Type: text/plain Date: 06 Jan 2003 17:35:58 -0600 Message-Id: <1041896173.1207.49.camel@granite.austin.ibm.com> Mime-Version: 1.0 Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: On Wed, 2002-12-18 at 18:06, Hollis Blanchard wrote: > > I need to mark the first kernel code page writeable because I need to > write to 0xc00000fc. Can someone tell me why the following code fails? > get_pteptr returns 0. > > addr = 0xc00000fc; > if (0 != get_pteptr(&init_mm, addr, &ptep)) { > /* mark it writable */ > *ptep = pte_mkwrite(*ptep); > /* flush this page from hw TLB */ > flush_tlb_range(&init_mm, addr, addr+1); > } else { > printk(KERN_ERR "couldn't get PTE!\n"); > } FYI: whoever added HIGHMEM support to mm/init.c:paging_init() already had this problem, and solved it by calling map_page(addr, 0, 0) first. I guess that the page is really not present in the software pagetable, and the map_page call forces it in: map_page(PKMAP_BASE, 0, 0); /* XXX gross */ pkmap_page_table = pte_offset(pmd_offset(pgd_offset_k(PKMAP_BASE), PKMAP_BASE), PKMAP_BASE); (get_pteptr just calls pte/pmd/pgd_offset with some error checking.) -Hollis -- PowerPC Linux IBM Linux Technology Center ** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/