Messages in this thread | | | Date | Wed, 17 Oct 2012 17:17:38 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] virtio: 9p: correctly pass physical address to userspace for high pages |
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On Wed, Oct 17, 2012 at 05:05:00PM +0100, Sasha Levin wrote: > On Wed, Oct 17, 2012 at 6:14 AM, Will Deacon <will.deacon@arm.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@rustcorp.com.au> > > Cc: Sasha Levin <levinsasha928@gmail.com> > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > > Signed-off-by: Will Deacon <will.deacon@arm.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.
This is *exactly* what I have observed. More specifically, I hacked kvmtool to support memory banks above 0x0 (I'll send some patches soon) so my PHYS_OFFSET was 0x80000000. virtio-9p then gave me physical addresses at 0x7fe02000, which if linearly mapped would be 0xffe02000 -- the pkmap!
> I'll plug it in and run tests on it.
The kernel-janitors list pointed out to me that we need to EXPORT_SYMBOL on kmap_to_page, so if you're building the virtio ring as a module you'll need to do that.
Cheers,
Will
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