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. If we're worried about space usage in the paca we can probably consolidate this and some other things into a flags word. cheers
