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[S390] s390-kvm: leave sie context on work. Removes preemption requirement

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From: Martin Schwidefsky <schwidefsky@de.ibm.com>

This patch fixes a bug with cpu bound guest on kvm-s390. Sometimes it
was impossible to deliver a signal to a spinning guest. We used
preemption as a circumvention. The preemption notifiers called
vcpu_load, which checked for pending signals and triggered a host
intercept. But even with preemption, a sigkill was not delivered
immediately.

This patch changes the low level host interrupt handler to check for the
SIE  instruction, if TIF_WORK is set. In that case we change the
instruction pointer of the return PSW to rerun the vcpu_run loop. The kvm
code sees an intercept reason 0 if that happens. This patch adds accounting
for these types of intercept as well.

The advantages:
- works with and without preemption
- signals are delivered immediately
- much better host latencies without preemption

Acked-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Christian Borntraeger
2008-05-07 09:22:53 +02:00
committed by Martin Schwidefsky
parent 2688905e6a
commit 0eaeafa10f
5 changed files with 34 additions and 6 deletions
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1
arch/s390/kvm/Kconfig
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@@ -22,7 +22,6 @@ config KVM
select PREEMPT_NOTIFIERS
select ANON_INODES
select S390_SWITCH_AMODE
select PREEMPT
---help---
Support hosting paravirtualized guest machines using the SIE
virtualization capability on the mainframe. This should work