Re: [PATCH v2 13/16] powerpc/watchpoint: Prepare handler to handle more than one watcnhpoint

[Christophe Leroy]

Le 01/04/2020 Ã 11:13, Ravi Bangoria a ÃcritÂ:
> On 4/1/20 12:20 PM, Christophe Leroy wrote:
> > Le 01/04/2020 Ã 08:13, Ravi Bangoria a ÃcritÂ:
> > > Currently we assume that we have only one watchpoint supported by hw.
> > > Get rid of that assumption and use dynamic loop instead. This should
> > > make supporting more watchpoints very easy.
> > >
> > > With more than one watchpoint, exception handler need to know which
> > > DAWR caused the exception, and hw currently does not provide it. So
> > > we need sw logic for the same. To figure out which DAWR caused the
> > > exception, check all different combinations of user specified range,
> > > dawr address range, actual access range and dawrx constrains. For ex,
> > > if user specified range and actual access range overlaps but dawrx is
> > > configured for readonly watchpoint and the instruction is store, this
> > > DAWR must not have caused exception.
> > >
> > > Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
> > > ---
> > > Â arch/powerpc/include/asm/processor.h |ÂÂ 2 +-
> > > Â arch/powerpc/include/asm/sstep.hÂÂÂÂ |ÂÂ 2 +
> > >  arch/powerpc/kernel/hw_breakpoint.c | 396 +++++++++++++++++++++------
> > > Â arch/powerpc/kernel/process.cÂÂÂÂÂÂÂ |ÂÂ 3 -
> > > Â 4 files changed, 313 insertions(+), 90 deletions(-)
> >
> > [...]
> >
> > > -static bool
> > > -dar_range_overlaps(unsigned long dar, int size, struct 
> > > arch_hw_breakpoint *info)
> > > +static bool dar_user_range_overlaps(unsigned long dar, int size,
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ struct arch_hw_breakpoint *info)
> > > Â {
> > > ÂÂÂÂÂ return ((dar <= info->address + info->len - 1) &&
> > > ÂÂÂÂÂÂÂÂÂ (dar + size - 1 >= info->address));
> > > Â }
> >
> > Here and several other places, I think it would be more clear if you 
> > could avoid the - 1 :
> >
> > ÂÂÂÂÂreturn ((dar < info->address + info->len) &&
> > ÂÂÂÂÂÂÂÂ (dar + size > info->address));
>
> Ok. see below...
>
> > > +static bool dar_in_hw_range(unsigned long dar, struct 
> > > arch_hw_breakpoint *info)
> > > +{
> > > +ÂÂÂ unsigned long hw_start_addr, hw_end_addr;
> > > +
> > > +ÂÂÂ hw_start_addr = ALIGN_DOWN(info->address, HW_BREAKPOINT_SIZE);
> > > +ÂÂÂ hw_end_addr = ALIGN(info->address + info->len, 
> > > HW_BREAKPOINT_SIZE) - 1;
> > > +
> > > +ÂÂÂ return ((hw_start_addr <= dar) && (hw_end_addr >= dar));
> > > +}
> >
> > ÂÂÂÂÂhw_end_addr = ALIGN(info->address + info->len, HW_BREAKPOINT_SIZE);
> >
> > ÂÂÂÂÂreturn ((hw_start_addr <= dar) && (hw_end_addr > dar));
>
> I'm using -1 while calculating end address is to make it
> inclusive. If I don't use -1, the end address points to a
> location outside of actual range, i.e. it's not really an
> end address.

But that's what is done is several places, for instance:

https://elixir.bootlin.com/linux/v5.6/source/arch/powerpc/mm/dma-noncoherent.c#L22

https://elixir.bootlin.com/linux/v5.6/source/arch/powerpc/include/asm/book3s/32/kup.h#L92

In several places like this, end is outside of the range. My feeling is 
that is helps with readability.

Christophe