On Fri, Oct 25, 2019 at 08:44:56AM +0200, Petr Mladek wrote: > On Thu 2019-10-24 15:16:34, Peter Zijlstra wrote: > > On Wed, Oct 23, 2019 at 12:00:25PM -0500, Josh Poimboeuf wrote: > > > > > > This then raises a number of questions: > > > > > > > > 1) why is that RELA (that obviously does not depend on any module) > > > > applied so late? > > > > > > Good question. The 'pv_ops' symbol is exported by the core kernel, so I > > > can't see any reason why we'd need to apply that rela late. In theory, > > > kpatch-build isn't supposed to convert that to a klp rela. Maybe > > > something went wrong in the patch creation code. > > > > > > I'm also questioning why we even need to apply the parainstructions > > > section late. Maybe we can remove that apply_paravirt() call > > > altogether, along with .klp.arch.parainstruction sections. > > Hmm, the original bug report against livepatching was actually about > paravirt ops, see below. Yes, I found that. > > > I'm not sure about alternatives, but maybe we can enforce such > > > limitations with tooling and/or kernel checks. > > > > Right, so on IRC you implied you might have some additional details on > > how alternatives were affected; did you manage to dig that up? > > I am not sure what Josh had in mind. But the problem with livepatches, > paravort ops, and alternatives was described in the related patchset, see > https://lkml.kernel.org/r/1471481911-5003-1-git-send-email-jeyu@xxxxxxxxxx Yes, and my complaint there is that that thread is void of useful content. > The original bug report is > https://lkml.kernel.org/r/20160329120518.GA21252@xxxxxxxxxxxxx I found the github (*groan*) link in the thread above. >From all that I could only make that the paravirt stuff is just doing it wrong (see earlier emails, core-kernel RELAs really should be applied at the time of patch-module load, there's no excuse for them to be delayed to the .klp.rela. section) at which point paravirt will also magically work. But none of that explains why apply_alternatives() is also delayed. So I'm very tempted to just revert that patchset for doing it all wrong.
