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

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Message-ID: <CACzsE9qka0j7vKm186Z70fhNy9L4dNR3B97-jQ2oZZAwYduaRw@mail.gmail.com>
Date:   Wed, 8 Jul 2020 17:44:25 +1000
From:   Jordan Niethe <jniethe5@...il.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>, mikey@...ling.org,
        apopple@...ux.ibm.com, Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        naveen.n.rao@...ux.vnet.ibm.com, peterz@...radead.org,
        jolsa@...nel.org, oleg@...hat.com, fweisbec@...il.com,
        mingo@...nel.org, pedromfc@...ibm.com, miltonm@...ibm.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/9] powerpc/watchpoint: Fix 512 byte boundary limit

On Wed, Jul 8, 2020 at 2:53 PM Ravi Bangoria
<ravi.bangoria@...ux.ibm.com> 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@...ibm.com>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> ---
>  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
>