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From: Bart Van Assche <bvanassche@acm.org>
To: Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Ming Lei <ming.lei@redhat.com>,
	 Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Ming Lei <tom.leiming@gmail.com>,
	linux-block <linux-block@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	"open list:XFS FILESYSTEM" <linux-xfs@vger.kernel.org>,
	Dave Chinner <dchinner@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jens Axboe <axboe@kernel.dk>, Christoph Lameter <cl@linux.com>,
	 Linus Torvalds <torvalds@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: block: DMA alignment of IO buffer allocated from slab
Date: Mon, 24 Sep 2018 09:19:44 -0700	[thread overview]
Message-ID: <1537805984.195115.14.camel@acm.org> (raw)
In-Reply-To: <10c706fd-2252-f11b-312e-ae0d97d9a538@virtuozzo.com>

On Mon, 2018-09-24 at 19:07 +0300, Andrey Ryabinin wrote:
> On 09/24/2018 06:58 PM, Bart Van Assche wrote:
> > On Mon, 2018-09-24 at 18:52 +0300, Andrey Ryabinin wrote:
> > > Yes, with CONFIG_DEBUG_SLAB=y, CONFIG_SLUB_DEBUG_ON=y kmalloc() guarantees
> > > that result is aligned on ARCH_KMALLOC_MINALIGN boundary.
> > 
> > Had you noticed that Vitaly Kuznetsov showed that this is not the case? See
> > also https://lore.kernel.org/lkml/87h8ij0zot.fsf@vitty.brq.redhat.com/.
> 
> I'm not following. On x86-64 ARCH_KMALLOC_MINALIGN is 8, all pointers that
> Vitaly Kuznetsov showed are 8-byte aligned.

Hi Andrey,

That means that two buffers allocated with kmalloc() may share a cache line on
x86-64. Since it is allowed to use a buffer allocated by kmalloc() for DMA, can
this lead to data corruption, e.g. if the CPU writes into one buffer allocated
with kmalloc() and a device performs a DMA write to another kmalloc() buffer and
both write operations affect the same cache line?

Thanks,

Bart.

  reply	other threads:[~2018-09-24 16:19 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-19  9:15 block: DMA alignment of IO buffer allocated from slab Ming Lei
2018-09-19  9:41 ` Vitaly Kuznetsov
2018-09-19  9:41   ` Vitaly Kuznetsov
2018-09-19  9:41   ` Vitaly Kuznetsov
2018-09-19 10:02   ` Ming Lei
2018-09-19 10:02     ` Ming Lei
2018-09-19 11:15     ` Vitaly Kuznetsov
2018-09-19 11:15       ` Vitaly Kuznetsov
2018-09-19 11:15       ` Vitaly Kuznetsov
2018-09-20  1:28       ` Ming Lei
2018-09-20  3:59         ` Yang Shi
2018-09-20  6:32         ` Christoph Hellwig
2018-09-20  6:31 ` Christoph Hellwig
2018-09-21 13:04   ` Vitaly Kuznetsov
2018-09-21 13:04     ` Vitaly Kuznetsov
2018-09-21 13:04     ` Vitaly Kuznetsov
2018-09-21 13:05     ` Christoph Hellwig
2018-09-21 15:00       ` Jens Axboe
2018-09-24 16:06       ` Christopher Lameter
2018-09-24 17:49         ` Jens Axboe
2018-09-24 18:00           ` Christopher Lameter
2018-09-24 18:09             ` Jens Axboe
2018-09-25  7:49               ` Dave Chinner
2018-09-25 15:44                 ` Jens Axboe
2018-09-25 21:04                 ` Matthew Wilcox
2018-09-23 22:42     ` Ming Lei
2018-09-24  9:46       ` Andrey Ryabinin
2018-09-24 14:19         ` Bart Van Assche
2018-09-24 14:43           ` Andrey Ryabinin
2018-09-24 14:43             ` Andrey Ryabinin
2018-09-24 15:08             ` Bart Van Assche
2018-09-24 15:08               ` Bart Van Assche
2018-09-24 15:52               ` Andrey Ryabinin
2018-09-24 15:58                 ` Bart Van Assche
2018-09-24 15:58                   ` Bart Van Assche
2018-09-24 16:07                   ` Andrey Ryabinin
2018-09-24 16:19                     ` Bart Van Assche [this message]
2018-09-24 16:19                       ` Bart Van Assche
2018-09-24 16:47                       ` Christopher Lameter
2018-09-24 18:57                       ` Matthew Wilcox
2018-09-24 19:56                         ` Bart Van Assche
2018-09-24 19:56                           ` Bart Van Assche
2018-09-24 20:41                           ` Matthew Wilcox
2018-09-24 20:54                             ` Bart Van Assche
2018-09-24 20:54                               ` Bart Van Assche
2018-09-24 21:09                               ` Matthew Wilcox
2018-09-25  0:16                         ` Ming Lei
2018-09-25  3:28                           ` Matthew Wilcox
2018-09-25  4:10                             ` Bart Van Assche
2018-09-25  4:44                               ` Matthew Wilcox
2018-09-25  6:55                                 ` Ming Lei
2018-09-24 15:17           ` Christopher Lameter
2018-09-25  0:20             ` Ming Lei
2018-09-20 14:07 ` Bart Van Assche
2018-09-21  1:56 ` Dave Chinner
2018-09-21  1:56   ` Dave Chinner
2018-09-21  7:08   ` Christoph Hellwig
2018-09-21  7:25     ` Ming Lei
2018-09-21 14:59       ` Jens Axboe

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