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Re: [Xen-devel] Serial console problem with Xen 3.0

On 7 Apr 2006, at 15:44, Don Zickus wrote:

Me too. Adding "sync_console" at least repaired the console *output*. I
still have the problem that keyboard input does not reach linux, as it
seems. Here is my config:

Adding "pnpacpi=off" to the command line is our quick and dirty hack for now. Don't know the root cause yet, but at least it will get you going.

I have some suspicion that this, and the IRQ flooding issues that suse have been seeing, may be due to insufficient checking and translation and book-keeping at the ioapic management interface that Xen exports. See ioapic_guest_write() in xen/arch/x86/io_apic.c. Domain0 is responsible for IRQ steering and routing, and therefore for most of the management of IO-APICs, *but*: 1. Xen is responsible for masking/unmasking as part of normal interrupt servicing. 2. Xen may own some of the interrupts routed via the IO-APIC (serial and timer). Domain0 won't necessarily know about these and I think in the case of serial interrupt in particular it may end up screwing that IRQ line, in theory.

It may be worth getting Xen and XenLinux to dump verbose info about their view of IO-APIC state, and maybe add tracing to ioapic_guest_write() and see how domain0 is trying to drive the IO APICs. You may well see some IO APIC write coming thru just before the serial line goes dead. If so, the question will be whether the problem is due to broken checking/translating in Xen, or whether a fix is needed to dom0 ioapic code.

 -- Keir

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