linux-kernel - Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO

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Message-ID: <YrvvfpW4MmQiM47H@infradead.org>
Date:   Tue, 28 Jun 2022 23:21:50 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Michael Schmitz <schmitzmic@...il.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        scsi <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jakub Kicinski <kuba@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        Khalid Aziz <khalid@...ehiking.org>,
        "Maciej W . Rozycki" <macro@...am.me.uk>,
        Matt Wang <wwentao@...are.com>,
        Miquel van Smoorenburg <mikevs@...all.net>,
        Mark Salyzyn <salyzyn@...roid.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        alpha <linux-alpha@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        Denis Efremov <efremov@...ux.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Subject: Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS

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.