* Steven Rostedt ([EMAIL PROTECTED]) wrote: > > > On Mon, 18 Aug 2008, Mathieu Desnoyers wrote: > > > * Steven Rostedt ([EMAIL PROTECTED]) wrote: > > > > > > On Tue, 19 Aug 2008, Benjamin Herrenschmidt wrote: > > > > > > > > > > > > Hmm, this was originally copied from x86, where we did a cmpxchg, but > > > > > that > > > > > is probably not needed since all of this is done in kstop_machine. > > > > > Also, > > > > > only the "get" is needed. If we don't fault there, we wont fault on > > > > > the > > > > > put (unless we have permissions wrong, and that would be a bug). > > > > > > > > Would it ? How do we make sure the kernel text is mapped writeable ? > > > > > > We map it writeable if FTRACE is enabled. > > > > > > > Argh. See text_poke(). It's there exactly for this purpose on x86. > > > > OK, I just tried text_poke and it unfortunately fails. The problem is that > it requires that the text you are changing is aligned and fits on one > page. We have no control over that. > > -- Steve >
Ok, there are two cases where it's ok : 1 - in stop_machine, considering we are not touching code executed in NMI handlers. 2 - when using my replace_instruction_safe() which uses a temporary breakpoint when doing the instruction replacement. In those cases you could use text_poke_early(). See http://git.kernel.org/?p=linux/kernel/git/compudj/linux-2.6-lttng.git;a=blob;f=arch/x86/kernel/immediate.c;h=7789e2c75bf03e645f15759d5dff0c1698493f92;hb=HEAD For a use example. Basically it looks like : 360 pages[0] = virt_to_page((void *)bypass_eip); 361 vaddr = vmap(pages, 1, VM_MAP, PAGE_KERNEL); 362 BUG_ON(!vaddr); 363 text_poke_early(&vaddr[bypass_eip & ~PAGE_MASK], 364 (void *)addr, size); 365 /* 366 * Fill the rest with nops. 367 */ 368 len = NR_NOPS - size; 369 add_nops((void *) 370 &vaddr[(bypass_eip & ~PAGE_MASK) + size], 371 len); 372 print_dbg_bytes("inserted nops", 373 &vaddr[(bypass_eip & ~PAGE_MASK) + size], len); 374 vunmap(vaddr); Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
