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Re: [Xen-devel] Removing the PVH assert in arch/x86/hvm/io.c:87

On Thu, 4 Dec 2014 17:35:59 +0100
Roger Pau Monnà <roger.pau@xxxxxxxxxx> wrote:

> Hello,
> I've just stumbled upon this assert while testing PVH on different
> hardware. It was added in 7c4870 as a safe belt, but it turns out INS
> and OUTS go through handle_mmio. So using this instructions from a PVH
> guest basically kills Xen.

Right. Unf CR-moves/lmsw/clts intercepts also go thru handle_mmio, and
the suggestion was to clean it up first with another emulator function
for CR/IO intercepts. I attempted to do that before I left :


See also:


> I've removed it and everything seems fine, so I'm considering sending
> a patch for 4.5 in order to have it removed. I think the path that
> could trigger the crash because of the missing vioapic stuff is
> already guarded by the other chunk added in the same patch.

No, there used to be another path thru hvm_hap_nested_page_fault()
that would walk the back end handlers and crash xen. So you might
wanna check to make sure. I see hvm_hap_nested_page_fault() looks a
little different now, so not sure if its still broken... 


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