linux-kernel - Re: [PATCH] virtio: 9p: correctly pass physical address to userspace for high pages

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Message-ID: <CA+1xoqcjomrD05vxdgx4FG2wR8DTmV58Xk5=BeVD3JGVfWrssA@mail.gmail.com>
Date:	Wed, 17 Oct 2012 12:05:00 -0400
From:	Sasha Levin <levinsasha928@...il.com>
To:	Will Deacon <will.deacon@....com>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Marc Zyngier <marc.zyngier@....com>
Subject: Re: [PATCH] virtio: 9p: correctly pass physical address to userspace
 for high pages

On Wed, Oct 17, 2012 at 6:14 AM, Will Deacon <will.deacon@....com> wrote:
> When using a virtio transport, the 9p net device allocates pages to back
> the descriptors inserted into the virtqueue. These allocations may be
> performed from atomic context (under the channel lock) and can therefore
> return high mappings which aren't suitable for virt_to_phys.
>
> This patch ensures that virtual addresses for virtio queue descriptors
> are converted to physical addresses using kmap_to_page, which handles
> high memory correctly.
>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Sasha Levin <levinsasha928@...il.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---

One of the things I was seeing when fuzzing within lkvm were random
crashes resulting
from "odd" addresses used by virtio-9p queue descriptions. I
attributed that to memory
corruption as a result of something else failing the fuzz tests
before, but this patch
explains what might have gone wrong.

I'll plug it in and run tests on it.


Thanks,
Sasha
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