linux-kernel - Re: [PATCH] virtio_console: Stop doing DMA on the stack

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Message-ID: <20160908064943.GA25876@gmail.com>
Date:   Thu, 8 Sep 2016 08:49:43 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Amit Shah <amit.shah@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH] virtio_console: Stop doing DMA on the stack


* Amit Shah <amit.shah@...hat.com> wrote:

> On (Tue) 30 Aug 2016 [08:04:15], Andy Lutomirski wrote:
> > virtio_console uses a small DMA buffer for control requests.  Move
> > that buffer into heap memory.
> > 
> > Doing virtio DMA on the stack is normally okay on non-DMA-API virtio
> > systems (which is currently most of them), but it breaks completely
> > if the stack is virtually mapped.
> > 
> > Tested by typing both directions using picocom aimed at /dev/hvc0.
> > 
> > Signed-off-by: Andy Lutomirski <luto@...nel.org>
> 
> Looks fine,
> 
> Reviewed-by: Amit Shah <amit.shah@...hat.com>
> 
> > ---
> > 
> > Hi all-
> > 
> > This is currently broken in tip:x86/asm.  If you (Amit) like this patch,
> > would it make sense for Ingo to add it to -tip?
> 
> Yes, I'm fine with that.

Thanks! FYI, this patch now lives as:

  9472fe7040bb ("virtio_console: Stop doing DMA on the stack")

in tip:x86/asm, and is targeted for a v4.9 merge.

Thanks,

	Ingo