linux-kernel - Re: [PATCH 1/4] vfio: trivially use __aligned

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Message-ID: <ZNpoq7emI19fApND@ziepe.ca>
Date:   Mon, 14 Aug 2023 14:47:23 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Stefan Hajnoczi <stefanha@...hat.com>
Cc:     kvm@...r.kernel.org, "Tian, Kevin" <kevin.tian@...el.com>,
        linux-kernel@...r.kernel.org,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH 1/4] vfio: trivially use __aligned_u64 for ioctl structs

On Wed, Aug 09, 2023 at 05:02:45PM -0400, Stefan Hajnoczi wrote:
> u64 alignment behaves differently depending on the architecture and so
> <uapi/linux/types.h> offers __aligned_u64 to achieve consistent behavior
> in kernel<->userspace ABIs.
> 
> There are structs in <uapi/linux/vfio.h> that can trivially be updated
> to __aligned_u64 because the struct sizes are multiples of 8 bytes.
> There is no change in memory layout on any CPU architecture and
> therefore this change is safe.
> 
> The commits that follow this one handle the trickier cases where
> explanation about ABI breakage is necessary.
> 
> Suggested-by: Jason Gunthorpe <jgg@...pe.ca>
> Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
> ---
>  include/uapi/linux/vfio.h | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason