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

[Jordan Niethe]

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?

>                         return -EINVAL;
>         } else if (IS_ENABLED(CONFIG_PPC_8xx)) {
>                 /* 8xx can setup a range without limitation */
> --
> 2.26.2
>