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Date: Fri, 30 May 2014 08:41:00 -0700
Message-ID: <CA+55aFycqAw2AqQGv8aTPs_RxyKZqMdoyeSxWRSDk2N-PiBZeg@mail.gmail.com>
Subject: Re: [RFC 2/2] x86_64: expand kernel stack to 16K
From: Linus Torvalds <torvalds@linux-foundation.org>
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Sender: owner-linux-mm@kvack.org
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To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dave Chinner <david@fromorbit.com>, Minchan Kim <minchan@kernel.org>, Dave Jones <davej@redhat.com>, Jens Axboe <axboe@kernel.dk>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm <linux-mm@kvack.org>, Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>, Hugh Dickins <hughd@google.com>, Rusty Russell <rusty@rustcorp.com.au>, "Michael S. Tsirkin" <mst@redhat.com>, Dave Hansen <dave.hansen@intel.com>, Steven Rostedt <rostedt@goodmis.org>

On Fri, May 30, 2014 at 8:25 AM, H. Peter Anvin <hpa@zytor.com> wrote:
>
> If we removed struct thread_info from the stack allocation then one
> could do a guard page below the stack.  Of course, we'd have to use IST
> for #PF in that case, which makes it a non-production option.

We could just have the guard page in between the stack and the
thread_info, take a double fault, and then just map it back in on
double fault.

That would give us 8kB of "normal" stack, with a very loud fault - and
then an extra 7kB or so of stack (whatever the size of thread-info is)
- after the first time it traps.

That said, it's still likely a non-production option due to the page
table games we'd have to play at fork/clone time.

               Linus

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