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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Segher Boessenkool <segher@kernel.crashing.org>,
        Balbir Singh <bsingharora@gmail.com>
Cc:     erhard_f@mailbox.org, jack@suse.cz, linuxppc-dev@ozlabs.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        aneesh.kumar@linux.vnet.ibm.com
Subject: Re: [PATCH] powerpc/64s: Fix possible corruption on big endian due to pgd/pud_present()
In-Reply-To: <20190216142206.GE14180@gate.crashing.org>
References: <20190214062339.7139-1-mpe@ellerman.id.au> <20190216105511.GA31125@350D> <20190216142206.GE14180@gate.crashing.org>
Date:   Sun, 17 Feb 2019 19:34:36 +1100
Message-ID: <87bm3add9f.fsf@concordia.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Segher Boessenkool <segher@kernel.crashing.org> writes:

> Hi all,
>
> On Sat, Feb 16, 2019 at 09:55:11PM +1100, Balbir Singh wrote:
>> On Thu, Feb 14, 2019 at 05:23:39PM +1100, Michael Ellerman wrote:
>> > In v4.20 we changed our pgd/pud_present() to check for _PAGE_PRESENT
>> > rather than just checking that the value is non-zero, e.g.:
>> > 
>> >   static inline int pgd_present(pgd_t pgd)
>> >   {
>> >  -       return !pgd_none(pgd);
>> >  +       return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT));
>> >   }
>> > 
>> > Unfortunately this is broken on big endian, as the result of the
>> > bitwise && is truncated to int, which is always zero because
>
> (Bitwise "&" of course).

Thanks, I fixed that up.

cheers