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

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Date:   Fri, 9 Sep 2016 21:10:30 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Amit Shah <amit.shah@...hat.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_console: Stop doing DMA on the stack

On Thu, Sep 08, 2016 at 08:49:43AM +0200, Ingo Molnar wrote:
> 
> * 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

Thinking about it, maybe we should put it in 4.8
after all, for benefit of systems using DMA API with virtio.
Thoughts?