From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS
Date: Tue, 28 Jun 2022 23:21:50 -0700
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To: Michael Schmitz <schmitzmic@gmail.com>
Cc: Arnd Bergmann <arnd@kernel.org>, 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>

On Wed, Jun 29, 2022 at 11:09:00AM +1200, Michael Schmitz wrote:
> And all SCSI buffers are allocated using kmalloc? No way at all for user
> space to pass unaligned data?

Most that you will see actually comes from the page allocator.  But
the block layer has a dma_alignment limit, and when userspace sends
I/O that is not properly aligned it will be bounce buffered before
it it sent to the driver.