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[123.243.232.193]) by smtp.gmail.com with ESMTPSA id p12sm17159170pfj.81.2019.02.16.02.55.14 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 16 Feb 2019 02:55:15 -0800 (PST) Date: Sat, 16 Feb 2019 21:55:11 +1100 From: Balbir Singh To: Michael Ellerman Cc: linuxppc-dev@ozlabs.org, aneesh.kumar@linux.vnet.ibm.com, jack@suse.cz, erhard_f@mailbox.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] powerpc/64s: Fix possible corruption on big endian due to pgd/pud_present() Message-ID: <20190216105511.GA31125@350D> References: <20190214062339.7139-1-mpe@ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190214062339.7139-1-mpe@ellerman.id.au> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 Not sure why that should happen, why is the result an int? What causes the casting of pgd_t & be64 to be truncated to an int. > _PAGE_PRESENT is 0x8000000000000000ul. This means pgd_present() and > pud_present() are always false at compile time, and the compiler > elides the subsequent code. > > Remarkably with that bug present we are still able to boot and run > with few noticeable effects. However under some work loads we are able > to trigger a warning in the ext4 code: > > WARNING: CPU: 11 PID: 29593 at fs/ext4/inode.c:3927 .ext4_set_page_dirty+0x70/0xb0 > CPU: 11 PID: 29593 Comm: debugedit Not tainted 4.20.0-rc1 #1 > ... > NIP .ext4_set_page_dirty+0x70/0xb0 > LR .set_page_dirty+0xa0/0x150 > Call Trace: > .set_page_dirty+0xa0/0x150 > .unmap_page_range+0xbf0/0xe10 > .unmap_vmas+0x84/0x130 > .unmap_region+0xe8/0x190 > .__do_munmap+0x2f0/0x510 > .__vm_munmap+0x80/0x110 > .__se_sys_munmap+0x14/0x30 > system_call+0x5c/0x70 > > The fix is simple, we need to convert the result of the bitwise && to > an int before returning it. > > Thanks to Jan Kara and Aneesh for help with debugging. > > Fixes: da7ad366b497 ("powerpc/mm/book3s: Update pmd_present to look at _PAGE_PRESENT bit") > Cc: stable@vger.kernel.org # v4.20+ > Reported-by: Erhard F. > Reviewed-by: Aneesh Kumar K.V > Signed-off-by: Michael Ellerman > --- > arch/powerpc/include/asm/book3s/64/pgtable.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h > index c9bfe526ca9d..d8c8d7c9df15 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -904,7 +904,7 @@ static inline int pud_none(pud_t pud) > > static inline int pud_present(pud_t pud) > { > - return (pud_raw(pud) & cpu_to_be64(_PAGE_PRESENT)); > + return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PRESENT)); > } > > extern struct page *pud_page(pud_t pud); > @@ -951,7 +951,7 @@ static inline int pgd_none(pgd_t pgd) > > static inline int pgd_present(pgd_t pgd) > { > - return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT)); > + return !!(pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT)); > } > Care to put a big FAT warning, so that we don't repeat this again (as in authors planning on changing these bits). Balbir Singh.