On Sun, Jun 02, 2013 at 06:09:50PM +0300, Michael S. Tsirkin wrote:
On Sun, Jun 02, 2013 at 06:05:42PM +0300, Gleb Natapov wrote:
On Wed, May 29, 2013 at 11:45:44AM +0300, Michael S. Tsirkin wrote:
On Tue, May 28, 2013 at 07:53:09PM -0400, Kevin O'Connor wrote:
On Thu, May 23, 2013 at 03:41:32PM +0300, Michael S. Tsirkin wrote:
Juan is not available now, and Anthony asked for agenda to be sent early. So here comes:
Agenda for the meeting Tue, May 28:
- Generating acpi tables
I didn't see any meeting notes, but I thought it would be worthwhile to summarize the call. This is from memory so correct me if I got anything wrong.
Anthony believes that the generation of ACPI tables is the task of the firmware. Reasons cited include security implications of running more code in qemu vs the guest context, complexities in running iasl on big-endian machines, possible complexity of having to regenerate tables on a vm reboot, overall sloppiness of doing it in QEMU. Raised that QOM interface should be sufficient.
Kevin believes that the bios table code should be moved up into QEMU. Reasons cited include the churn rate in SeaBIOS for this QEMU feature (15-20% of all SeaBIOS commits since integrating with QEMU have been for bios tables; 20% of SeaBIOS commits in last year), complexity of trying to pass all the content needed to generate the tables (eg, device details, power tree, irq routing), complexity of scheduling changes across different repos and synchronizing their rollout, complexity of implemeting the code in both OVMF and SeaBIOS. Kevin wasn't aware of a requirement to regenerate acpi tables on a vm reboot.
I think this last one is based on a misunderstanding: it's based on assumption that we we change hardware by hotplug we should regenerate the tables to match. But there's no management that can take advantage of this. Two possible reasonable things we can tell management:
- hotplug for device XXX is not supported: restart qemu to make guest use the device
- hotplug for device XXX is supported
What is proposed here instead is a third option:
- hotplug is supported but device is not functional. reboot guest to make it fully functional
This will naturally lead to requirement to regenerate tables on reset.
And this is what would happen with guest-generated tables, and I consider this a bug, not a feature.
+1. This will probably break guest resume too.
If you really wanted to update tables dynamically, without restarting qemu, don't stop there, add an interface for guest to update them without reset. I think that's over-endineering and a requirement that's best avoided.
There were discussions on potentially introducing a middle component to generate the tables. Coreboot was raised as a possibility, and David thought it would be okay to use coreboot for both OVMF and SeaBIOS. The possibility was also raised of a "rom" that lives in the qemu repo, is run in the guest, and generates the tables (which is similar to the hvmloader approach that Xen uses).
Anthony requested that patches be made that generate the ACPI tables in QEMU for the upcoming hotplug work, so that they could be evaluated to see if they truly do need to live in QEMU or if the code could live in the firmware. There were no objections.
I volunteered to implement this.
Why hotplug should generate ACPI code? It does not do so on real HW.
Hotplug should not generate ACPI code. What is meant here is adding ACPI code to support hotplug of devices behind a PCI to PCI bridge.
Ah, OK. This one does not change on reset.