On Thu, 2016-03-24 at 14:42 +0100, Torsten Duwe wrote: > On Thu, Mar 24, 2016 at 10:04:05PM +1100, Michael Ellerman wrote:
> > +livepatch_handler: > > + CURRENT_THREAD_INFO(r12, r1) > [...] > > + /* Put ctr in r12 for global entry and branch there */ > > + mfctr r12 > > + bctrl > ^ > I like this piece. No need to fiddle out the return helper address. Good. > > + /* > > + * Now we are returning from the patched function to the original > > + * caller A. We are free to use r0 and r12, and we can use r2 until we > > + * restore it. > > + */ > > + > > + CURRENT_THREAD_INFO(r12, r1) > > + > > + /* Save stack pointer into r0 */ > > + mr r0, r1 > > + > > + ld r1, TI_livepatch_sp(r12) > > + > > + /* Check stack marker hasn't been trashed */ > > + lis r2, STACK_END_MAGIC@h > > + ori r2, r2, STACK_END_MAGIC@l > > + ld r12, -8(r1) > > +1: tdne r12, r2 > > + EMIT_BUG_ENTRY 1b, __FILE__, __LINE__ - 1, 0 > > This however worries me a bit. Sure, in the end, a stack overflow is > a stack overflow, and if all the information does not fit there, > there's little you can do. Yeah stack overflow in the kernel is very very fatal. > But wouldn't it be better to kmalloc that area and realloc in > klp_arch_set_pc when it's full? Maybe along with a warning message? You can't realloc in klp_arch_set_pc(), you might be patching sl*b and holding one of its locks. You might also recurse. We could allocate a larger buffer as a "klp stack" for each task when the first live patch is installed, and for every task created afterward. But that potentially significantly increases memory usage on live patched kernels :) > That way a live patched kernel will not run into stack size problems > any earlier than an unpatched kernel would. Yeah that's true. I'm not sure what the best trade off is. cheers _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
