On Thu, Mar 31, 2022 at 11:24 AM Mark Rutland <mark.rutland@xxxxxxx> wrote: > > On Wed, Mar 23, 2022 at 04:32:53PM +0100, andrey.konovalov@xxxxxxxxx wrote: > > From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > > > > Instead of trying to retrieve the SCS pointers from the stack, change > > interrupt handlers (for hard IRQ, Normal and Critical SDEI) to save the > > previous SCS pointer in a per-CPU variable. > > I'm *really* not keen on *always* poking this in the entry code for the > uncommon case of unwind. It complicates the entry code and means we're always > paying a cost for potentially no benefit. At a high-level, I don't think this > is the right approach. This also gives a 5% slowdown, which is not acceptable. What we can do instead, is to not collect frames from the higher exception levels at all. This would leave SCS-based stack collection method impaired, but this is probably fine for KASAN's use case: currently, stack depot filters out higher-level frames anyway, so KASAN never saves them. And the lower-level part of the stack trace is enough to identify the allocation. Thanks! > For the regular unwinder, I want to rework things such that we can identify > exception boundaries and look into the regs (e.g. so that we can recover the > PC+LR+FP and avoid duplicating part of this in a frame record), and I'd much > prefer that we did the same here.
