linux-kernel - Re: [RFC] fixing the UML failure root cause

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Message-ID: <CA+55aFyMXgzywjXCtS1a5F-BDu_XP4ecg3Tw7zLuawZs0QNYaw@mail.gmail.com>
Date:	Thu, 13 Oct 2011 18:19:16 +1200
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Lutomirski <luto@....edu>
Cc:	Ingo Molnar <mingo@...e.hu>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Adrian Bunk <bunk@...sta.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] fixing the UML failure root cause

On Wed, Oct 12, 2011 at 5:24 AM, Andrew Lutomirski <luto@....edu> wrote:
>
> So here's a different approach.  It's not perfect: it always blames
> SEGV_MAPERR instead of SEGV_ACCERR.  I implemented it for vgettimeofday
> but not the other two vsyscalls.
>
> What do you think of this approach?  If it seems good, I'll finish the
> patch and submit it.

I think the approach is valid, but you should *not* do this as some
kind of crazy byte-by-byte copy_to_user() emulation.

Do the "copy tz to user mode" as individual "put_user()" calls for
tv_sec/tv_usec/timezone. IOW, there are three words being written to
user mode, not "two memcpy's".

Other than that, there doesn't seem to be anything wrong.

            Linus
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