On Mon, Nov 28, 2022 at 11:59:37AM +0000, Tomislav Novak wrote:
> On Tue, Nov 15, 2022 at 03:09:37PM +0000, Catalin Marinas wrote:
> > > On ARM platforms is_default_overflow_handler() is used to determine if
> > > hw_breakpoint code should single-step over the watchpoint trigger or
> > > let the custom handler deal with it.
> > >
> > > Attaching a BPF program to a watchpoint replaces the handler with
> > > bpf_overflow_handler, which isn't recognized as a default handler so we
> > > never step over the instruction triggering the data abort exception (the
> > > watchpoint keeps firing):
> > >
> > > # bpftrace -e 'watchpoint:0x10000000:4:w { printf("hit\n"); }' ./wp_test
> > > Attaching 1 probe...
> > > hit
> > > hit
> > > hit
> > > [...]
> > >
> > > (wp_test performs a single 4-byte store to address 0x10000000)
> > >
> > > This patch replaces the check with uses_default_overflow_handler(), which
> > > accounts for the bpf_overflow_handler() case by also testing if the handler
> > > invokes one of the perf_event_output functions via orig_default_handler.
> > >
> > > Signed-off-by: Tomislav Novak <tnovak@xxxxxx>
> > > Tested-by: Samuel Gosselin <sgosselin@xxxxxx> # arm64
> > > ---
> > > arch/arm/kernel/hw_breakpoint.c | 8 ++++----
> > > arch/arm64/kernel/hw_breakpoint.c | 4 ++--
> > > include/linux/perf_event.h | 22 +++++++++++++++++++---
> > > 3 files changed, 25 insertions(+), 9 deletions(-)
> >
> > It looks like this slipped through the cracks. I'm fine with the patch
> > but could you split the arm and arm64 parts in separate patches? Unless
> > rmk acks it and we can take the patch through the arm64 (or perf) tree.
>
> Thanks for reviewing!
>
> Given the changes in the arch-independent perf_event.h, I think merging it
> as a single commit may be easiest (assuming rmk acks it).
>
> Alternatively I could move arm changes into a separate patch, keeping arm64
> and perf_event.h in this one (possibly splitting out the latter into its own
> commit). One that's merged, the arm patch could be submitted to linux-arm.
> What would you prefer?
Actually, arch/arm*/kernel/hw_breakpoint.c come under the ARM PMU
profiling, so no need to split the patch. It may need an ack from the
generic perf maintainers for include/linux/perf.h.
FWIW,
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
