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. Thanks, Nick
