Avi Kivity wrote:
On 07/22/2010 03:53 PM, Andre Przywara wrote:
Hi,
I found a regression with pvclock and SMP KVM _guests_.
PVCLOCK enabled guest kernels boot with qemu-kvm.git and with smp=1,
but with smp=2 halt at:
Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
(last line shown)
I bisected this down to:
commit 489fb490dbf8dab0249ad82b56688ae3842a79e8
Author: Glauber Costa <glommer@xxxxxxxxxx>
Date: Tue May 11 12:17:40 2010 -0400
x86, paravirt: Add a global synchronization point for pvclock
One commit before works, smp=1 always works, disabling PVCLOCK works.
Using qemu-kvm-0.12.4 works, too.
Having PVCLOCK enabled and with smp=2 the kernel halts without any
further message.
This is still the case with the lastest tip.
Even pinning both VCPU threads to the same host core show the bug.
The bug triggers on all hosts I tested, an single socket quadcore
Athlon, a dual socket dualcore K8-Opteron and a quad socket 12core
Opteron.
Please note that this is the guest kernel, the host kernel does not
matter.
I have no idea (and don't feel like ;-) debugging this, so I hope
someone will find and fix the bug.
Does this go away with CONFIG_DEBUG_RODATA=n? If so, it's a known bug
in the atomic_*() clobber lists.
Unfortunately the bug persists even with CONFIG_DEBUG_RODATA disabled.
The debug options I had enabled now are:
CONFIG_DEBUG_DEVRES=y
CONFIG_DEBUG_FS=y
CONFIG_DEBUG_KERNEL=y
CONFIG_DEBUG_BUGVERBOSE=y
CONFIG_DEBUG_MEMORY_INIT=y
CONFIG_DEBUG_STACKOVERFLOW=y
CONFIG_DEBUG_BOOT_PARAMS=y
I even disabled all kernel debug options, that does not help, too.
Regards,
Andre.
--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448-3567-12
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