linux-kernel - Re: Commit 'iomap: add support for dma aligned direct-io' causes qemu/KVM boot failures

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Message-ID: <20220929163931.GA10232@lst.de>
Date:   Thu, 29 Sep 2022 18:39:31 +0200
From:   Christoph Hellwig <hch@....de>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        qemu-devel@...gnu.org, kvm@...r.kernel.org,
        Kevin Wolf <kwolf@...hat.com>
Subject: Re: Commit 'iomap: add support for dma aligned direct-io' causes
 qemu/KVM boot failures

On Thu, Sep 29, 2022 at 10:37:22AM -0600, Keith Busch wrote:
> I don't think so. Memory alignment and length granularity are two completely
> different concepts. If anything, the kernel's ABI had been that the length
> requirement was also required for the memory alignment, not the other way
> around. That usage will continue working with this kernel patch.

Well, Linus does treat anything that breaks significant userspace
as a regression.  Qemu certainly is significant, but that might depend
on bit how common configurations hitting this issue are.