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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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