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Date:   Wed, 15 Jan 2020 17:59:57 +0100
From:   Eugene Syromiatnikov <esyr@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        "Dmitry V. Levin" <ldv@...linux.org>
Subject: Re: [PATCH] io_uring: fix compat for IORING_REGISTER_FILES_UPDATE

On Wed, Jan 15, 2020 at 09:53:27AM -0700, Jens Axboe wrote:
> We'd need it in a union for this to work.

Note that union usage may be a bit problematic, as it may lead to difference
in behaviour (and possible subtle bugs, as a result) between native 32-bit
kernel and 64-bit one in compat mode due to the fact that u64_to_user_ptr
doesn't check higher 32 bits on 32 bit kernels; it is mostly ignored
in the case of plain __u64 usage, as it is less likely to pass garbage
in the higher 32 bits in that case, but the issue, nevertheless, stands,
so I'd propose to check these bits in case the union approach
is implemented.

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