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xen-devel
Re: [Xen-devel] [PATCH] Calculate correct instruction length for data-fa
On 29 Apr 2006, at 02:20, Leendert van Doorn wrote:
The only difficulty is that the hypervisor keeps some of the device
state vpit and *pics and shotcuts operations to them. This state needs
to be exposed to qemu-dm so that it is saved and restored on every
qemu-dm invocation. I need to verify this, but as far as I'm aware, all
the accesses to the devices emulated in the hypervisor are PIO
operations. These are easy to decode with the exit information that is
provided by VT-x and SVM, so they don't need a a full instruction
decoder.
The APIC and IO-APIC are accessed via mmio. The former is written
fairly frequently with singleton updates (to the TPR and EOI registers)
so we'd want to carry on dealing with those directly in Xen I should
think. Still you'd have to deal with the case that one of the
Xen-emulated devices is accessed while emulating in qemu-dm -- as you
say you'd probably have to pull their state vectors out of Xen when
starting emulating. We'll need that for save/restore anyway though.
I don't know if this will make sense for emulated I/O but it does sound
like a very sane alternative to vmxassist for dealing with real mode.
-- Keir
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