On Wed, Jul 15, 2020 at 12:08:08PM +0200, Joerg Roedel wrote: > On Wed, Jul 15, 2020 at 11:51:36AM +0200, Peter Zijlstra wrote: > > On Wed, Jul 15, 2020 at 11:13:37AM +0200, Joerg Roedel wrote: > > > Then my understanding of intrumentation_begin/end() is wrong, I thought > > > that the kernel will forbid setting breakpoints before > > > instrumentation_begin(), which is necessary here because a break-point > > > in the #VC handler might cause recursive #VC-exceptions when #DB is > > > intercepted. > > > Maybe you can elaborate on why this makes no sense? > > > > Kernel avoids breakpoints in any noinstr text, irrespective of > > instrumentation_begin(). > > > > instrumentation_begin() merely allows one to call !noinstr functions. > > Right, but the handler calls into various other functions. I actually > started to annotate them all with noinstr, but that was a can of worms > when calling into generic kernel functions. And the only problem with > intrumentation in the #VC handler is the #VC-for-#DB exit-code, so I > decided to only handle this one with instrumentation forbidden and allow > it for the rest of the handler. OK, then maybe change the comment to something like: /* * Handle #DB before calling any !noinstr code to avoid * recursive #DB. */ ?
