Re: [PATCH 07/15] powerpc/watchpoint: Get watchpoint count dynamically while disabling them

[Ravi Bangoria]

On 3/18/20 12:27 PM, Ravi Bangoria wrote:
> On 3/17/20 4:02 PM, Christophe Leroy wrote:
> > Le 09/03/2020 Ã 09:57, Ravi Bangoria a ÃcritÂ:
> > > Instead of disabling only one watchpooint, get num of available
> > > watchpoints dynamically and disable all of them.
> > >
> > > Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
> > > ---
> > > Â arch/powerpc/include/asm/hw_breakpoint.h | 15 +++++++--------
> > > Â 1 file changed, 7 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
> > > index 980ac7d9f267..ec61e2b7195c 100644
> > > --- a/arch/powerpc/include/asm/hw_breakpoint.h
> > > +++ b/arch/powerpc/include/asm/hw_breakpoint.h
> > > @@ -75,14 +75,13 @@ extern void ptrace_triggered(struct perf_event *bp,
> > > ÂÂÂÂÂÂÂÂÂÂÂÂÂ struct perf_sample_data *data, struct pt_regs *regs);
> > > Â static inline void hw_breakpoint_disable(void)
> > > Â {
> > > -ÂÂÂ struct arch_hw_breakpoint brk;
> > > -
> > > -ÂÂÂ brk.address = 0;
> > > -ÂÂÂ brk.type = 0;
> > > -ÂÂÂ brk.len = 0;
> > > -ÂÂÂ brk.hw_len = 0;
> > > -ÂÂÂ if (ppc_breakpoint_available())
> > > -ÂÂÂÂÂÂÂ __set_breakpoint(&brk, 0);
> > > +ÂÂÂ int i;
> > > +ÂÂÂ struct arch_hw_breakpoint null_brk = {0};
> > > +
> > > +ÂÂÂ if (ppc_breakpoint_available()) {
> >
> > I think this test should go into nr_wp_slots() which should return zero when no breakpoint is available.
>
> Seems possible. Will change it in next version.

Once we move ppc_breakpoint_available() logic into nr_wp_slots(),
'dawr_force_enable' variable is checked in nr_wp_slots() before
it gets initialized in dawr_force_setup():

    start_kernel()
    |-> perf_event_init()
    |     init_hw_breakpoint()
    |       hw_breakpoint_slots()
    |         nr_wp_slots()
    |           /* Check dawr_force_enable variable */
    |
    |-> arch_call_rest_init()
          rest_init()
            kernel_thread(kernel_init, ...)
              ...
                kernel_init()
                  kernel_init_freeable()
                    ...
                    do_one_initcall()
                      dawr_force_setup()
                        /* Set dawr_force_enable = true */

Because of this, hw-breakpoint infrastructure is initialized with
no DAWRs. So I'm thinking to keep the code as it is i.e. not moving
ppc_breakpoint_available() test inside nr_wp_slots().

Ravi