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

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Message-ID: <YzXJwmP8pa3WABEG@kbusch-mbp.dhcp.thefacebook.com>
Date:   Thu, 29 Sep 2022 10:37:22 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     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 07:16:29PM +0300, Maxim Levitsky wrote:
> On Thu, 2022-09-29 at 09:48 -0600, Keith Busch wrote:
> > I am aware, and I've submitted the fix to qemu here:
> > 
> >   https://lists.nongnu.org/archive/html/qemu-block/2022-09/msg00398.html
> > 
> 
> 
> Thanks for quick response!
> 
> Question is though, isn't this an kernel ABI breakage?

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.