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Re: [Qemu-devel] PCI access virtualization
From: |
Mark Williamson |
Subject: |
Re: [Qemu-devel] PCI access virtualization |
Date: |
Thu, 5 Jan 2006 17:40:48 +0000 |
User-agent: |
KMail/1.9.1 |
> - IRQ sharing. Sharing host IRQs between native and virtualized devices is
> hard because the host needs to ack the interrupt in the IRQ handler, but
> doesn't really know how to do that until after it's run the guest to see
> what that does.
Could maybe have the (inevitable) kernel portion of the code grab the
interrupt, and not ack it until userspace does an ioctl on a special file (or
something like that?). There are patches floating around for userspace IRQ
handling, so I guess that could work.
> - DMA. qemu needs to rewrite DMA requests (in both directions) because the
> guest physical memory won't be at the same address on the host. Inlike ISA
> where there's a fixed DMA engine, I don't think there's any general way of
I was under the impression that you could get reasonably far by emulating a
few of the most popular commercial DMA engine chips and reissuing
address-corrected commands to the host. I'm not sure how common it is for
PCI cards to use custom DMA chips instead, though...
> There are patches that allow virtualization of PCI devices that don't use
> either of the above features. It's sufficient to get some Network cards
> working, but that's about it.
I guess PIO should be easy to work in any case.
> > I vaguely heard of a feature present in Xen, which allows to assign PCI
> > devices to one of the guests. I understand Xen works different than
> > QEMU, but maybe is would be possible to implement something similar.
>
> Xen is much easier because it cooperates with the host system (ie. xen), so
> both the above problems can be solved by tweaking the guest OS drivers/PCI
> subsystem setup.
Yep, XenLinux redefines various macros that were already present to do
guest-physical <-> host-physical address translations, so DMA Just Works
(TM).
> If you're testing specific drivers you could probably augment these drivers
> to pass the extra required information to qemu. ie. effectively use a
> special qemu pseudo-PCI interface rather than the normal piix PCI
> interface.
How about something like this?:
I'd imagine you could get away with a special header file with different macro
defines (as for Xen, above), just in the driver in question, and a special
"translation device / service" available to the QEmu virtual machine - could
be as simple as "write the guest physical address to an IO port, returns the
real physical address on next read". The virt_to_bus (etc) macros would use
the translation service to perform the appropriate translation at runtime.
Cheers,
Mark
- [Qemu-devel] PCI access virtualization, Michael Renzmann, 2006/01/05
- Re: [Qemu-devel] PCI access virtualization, Paul Brook, 2006/01/05
- Re: [Qemu-devel] PCI access virtualization,
Mark Williamson <=
- Re: [Qemu-devel] PCI access virtualization, Paul Brook, 2006/01/05
- Re: [Qemu-devel] PCI access virtualization, Jim C. Brown, 2006/01/05
- Re: [Qemu-devel] PCI access virtualization, Mark Williamson, 2006/01/05
- Re: [Qemu-devel] PCI access virtualization, Paul Brook, 2006/01/06
- Re: [Qemu-devel] PCI access virtualization, Mark Williamson, 2006/01/06
Re: [Qemu-devel] PCI access virtualization, Mark Williamson, 2006/01/05