On Tue, 20 Mar 2018 09:34:43 +1100 Michael Ellerman <m...@ellerman.id.au> wrote:
> Nicholas Piggin <npig...@gmail.com> writes: > > > On Mon, 19 Mar 2018 14:43:00 +0530 > > "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote: > > > >> We have some C code that we call into from real mode where we cannot > >> take any exceptions. Though the C functions themselves are mostly safe, > >> if these functions are traced, there is a possibility that we may take > >> an exception. For instance, in certain conditions, the ftrace code uses > >> WARN(), which uses a 'trap' to do its job. > >> > >> For such scenarios, introduce a new field in paca 'ftrace_disabled', > >> which is checked on ftrace entry before continuing. This field can then > >> be set to a non-zero value to disable/pause ftrace, and reset to zero to > >> resume ftrace. > >> > >> Since KVM is the only user for this currently, we guard the > >> ftrace/mcount checks within CONFIG_KVM. This can later be removed > >> if/when there are other users. > > > > Why not test HSTATE_IN_GUEST then? Add ftrace_disabled if non-KVM users > > come along. > > We want to use it for the kexec down path, we've already had bugs there. > > So please keep the separate flag and pull it out of #ifdef KVM. Okay that's fine. > If we're worried about space usage in the paca we can probably > consolidate this and some other things into a flags word. I'm not too concerned about some more u8 flags. Thanks, Nick
