From: David Laight <David.Laight@ACULAB.COM>
To: 'Michael Schmitz' <schmitzmic@gmail.com>,
Arnd Bergmann <arnd@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
scsi <linux-scsi@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>, Jakub Kicinski <kuba@kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Linux IOMMU <iommu@lists.linux-foundation.org>,
Khalid Aziz <khalid@gonehiking.org>,
"Maciej W . Rozycki" <macro@orcam.me.uk>,
Matt Wang <wwentao@vmware.com>,
Miquel van Smoorenburg <mikevs@xs4all.net>,
Mark Salyzyn <salyzyn@android.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux-Arch <linux-arch@vger.kernel.org>,
alpha <linux-alpha@vger.kernel.org>,
linux-m68k <linux-m68k@lists.linux-m68k.org>,
Parisc List <linux-parisc@vger.kernel.org>,
Denis Efremov <efremov@linux.com>,
"Michael Ellerman" <mpe@ellerman.id.au>,
John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Subject: RE: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS
Date: Thu, 30 Jun 2022 08:04:43 +0000 [thread overview]
Message-ID: <26852797d822462abc1c9f96def7fa42@AcuMS.aculab.com> (raw)
In-Reply-To: <9f812d3d-0fcd-46e6-6d7e-6d4bf66f24ab@gmail.com>
From: Michael Schmitz
> Sent: 29 June 2022 00:09
>
> Hi Arnd,
>
> On 29/06/22 09:50, Arnd Bergmann wrote:
> > On Tue, Jun 28, 2022 at 11:03 PM Michael Schmitz <schmitzmic@gmail.com> wrote:
> >> On 28/06/22 19:03, Geert Uytterhoeven wrote:
> >>>> The driver allocates bounce buffers using kmalloc if it hits an
> >>>> unaligned data buffer - can such buffers still even happen these days?
> >>> No idea.
> >> Hmmm - I think I'll stick a WARN_ONCE() in there so we know whether this
> >> code path is still being used.
> > kmalloc() guarantees alignment to the next power-of-two size or
> > KMALLOC_MIN_ALIGN, whichever is bigger. On m68k this means it
> > is cacheline aligned.
>
> And all SCSI buffers are allocated using kmalloc? No way at all for user
> space to pass unaligned data?
I didn't think kmalloc() gave any such guarantee about alignment.
There are cache-line alignment requirements on systems with non-coherent
dma, but otherwise the alignment can be much smaller.
One of the allocators adds a header to each item, IIRC that can
lead to 'unexpected' alignments - especially on m68k.
dma_alloc_coherent() does align to next 'power of 2'.
And sometimes you need (eg) 16k allocates that are 16k aligned.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-06-30 8:04 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-17 12:57 [PATCH v2 0/3] phase out CONFIG_VIRT_TO_BUS Arnd Bergmann
2022-06-17 12:57 ` [PATCH v2 1/3] scsi: dpt_i2o: drop stale VIRT_TO_BUS dependency Arnd Bergmann
2022-06-21 8:43 ` Hannes Reinecke
2022-06-17 12:57 ` [PATCH v2 2/3] scsi: BusLogic remove bus_to_virt Arnd Bergmann
2022-06-17 14:02 ` Robin Murphy
2022-06-21 8:45 ` Hannes Reinecke
2022-06-21 21:56 ` Khalid Aziz
2022-06-23 14:47 ` Arnd Bergmann
2022-06-24 15:38 ` Khalid Aziz
2022-06-24 15:43 ` Arnd Bergmann
2022-06-17 12:57 ` [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS Arnd Bergmann
2022-06-18 1:06 ` Michael Schmitz
2022-06-24 9:10 ` Arnd Bergmann
2022-06-26 5:21 ` Michael Schmitz
2022-06-26 8:36 ` Arnd Bergmann
2022-06-27 8:09 ` Michael Schmitz
2022-06-27 8:26 ` Geert Uytterhoeven
2022-06-27 21:12 ` Michael Schmitz
2022-06-28 3:25 ` Michael Schmitz
2022-06-28 7:03 ` Geert Uytterhoeven
2022-06-28 21:03 ` Michael Schmitz
2022-06-28 21:50 ` Arnd Bergmann
2022-06-28 23:09 ` Michael Schmitz
2022-06-28 23:50 ` Bart Van Assche
2022-06-29 0:01 ` Michael Schmitz
2022-06-29 0:14 ` Michael Schmitz
2022-06-29 6:21 ` Christoph Hellwig
2022-06-30 19:21 ` Michael Schmitz
2022-06-30 8:04 ` David Laight [this message]
2022-06-30 9:40 ` Christophe Leroy
2022-06-30 10:32 ` David Laight
2022-06-28 7:08 ` Arnd Bergmann
2022-06-28 21:38 ` Michael Schmitz
2022-06-28 21:55 ` Arnd Bergmann
2022-06-28 23:43 ` Michael Schmitz
2022-06-29 6:25 ` Christoph Hellwig
2022-06-30 19:26 ` Michael Schmitz
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