Re: Removing the PVH assert in arch/x86/hvm/io.c:87

["Jan Beulich" <JBeulich@suse.com>]

>>> On 04.12.14 at 17:35, <roger.pau@citrix.com> wrote:
> 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.
> 
> 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.

Iirc we settled on forbidding paths to handle_mmio() for PVH (hence
the ASSERT()). Sadly you provide way too little detail on what is
actually happening in your case: What's the use case of to-be-
emulated INS/OUTS in a PVH kernel? What's the call tree that gets
you into handle_mmio(), considering that both calls to
handle_mmio_with_translation() from hvm_hap_nested_page_fault()
as well as the one to handle_mmio() ought to be unreachable for PVH?

Jan