Re: [PATCH v3 1/9] powerpc/watchpoint: Fix 512 byte boundary limit

[Christophe Leroy]

Le 08/07/2020 Ã 09:44, Jordan Niethe a ÃcritÂ:
> On Wed, Jul 8, 2020 at 2:53 PM Ravi Bangoria
> <ravi.bangoria@xxxxxxxxxxxxx> wrote:
> > Milton Miller reported that we are aligning start and end address to
> > wrong size SZ_512M. It should be SZ_512. Fix that.
> >
> > While doing this change I also found a case where ALIGN() comparison
> > fails. Within a given aligned range, ALIGN() of two addresses does not
> > match when start address is pointing to the first byte and end address
> > is pointing to any other byte except the first one. But that's not true
> > for ALIGN_DOWN(). ALIGN_DOWN() of any two addresses within that range
> > will always point to the first byte. So use ALIGN_DOWN() instead of
> > ALIGN().
> >
> > Fixes: e68ef121c1f4 ("powerpc/watchpoint: Use builtin ALIGN*() macros")
> > Reported-by: Milton Miller <miltonm@xxxxxxxxxx>
> > Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
> > ---
> >   arch/powerpc/kernel/hw_breakpoint.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
> > index 0000daf0e1da..031e6defc08e 100644
> > --- a/arch/powerpc/kernel/hw_breakpoint.c
> > +++ b/arch/powerpc/kernel/hw_breakpoint.c
> > @@ -419,7 +419,7 @@ static int hw_breakpoint_validate_len(struct arch_hw_breakpoint *hw)
> >          if (dawr_enabled()) {
> >                  max_len = DAWR_MAX_LEN;
> >                  /* DAWR region can't cross 512 bytes boundary */
> > -               if (ALIGN(start_addr, SZ_512M) != ALIGN(end_addr - 1, SZ_512M))
> > +               if (ALIGN_DOWN(start_addr, SZ_512) != ALIGN_DOWN(end_addr - 1, SZ_512))
> I wonder if you should use end_addr - 1, but rather end_addr. For example:
> 512 -> 1023, because of the -1, 1024 will now be included in this
> range meaning 513 bytes?

end_addr is not part of the range.

If you want the range [512;1023], it means addr 512 len 512, that is 
end_addr = addr + len = 1024

Christophe