linux-kernel - Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put

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Message-ID: <CA+8MBb+Vubsx3Qyav25tgUgiGbs1XmEwoaCXTM=8jk4m2CxRbw@mail.gmail.com>
Date:   Mon, 7 Oct 2019 12:49:19 -0700
From:   Tony Luck <tony.luck@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Guenter Roeck <linux@...ck-us.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user()

On Mon, Oct 7, 2019 at 12:09 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> Hmm? I thought ia64 did unaligneds ok.

If PSR.ac is set, we trap. If it isn't set, then model specific
(though all implementations will
trap for an unaligned access that crosses a 4K boundary).

Linux sets PSR.ac. Applications can use prctl(PR_SET_UNALIGN) to choose whether
they want the kernel to silently fix things or to send SIGBUS.

Kernel always noisily (rate limited) fixes up unaligned access.

Your patch does make all the messages go away.

Tested-by: Tony Luck <tony.luck@...el.com>