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KVM: s390: bugfix for kvm/master (4.2)

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Here is a bugfix for a regression that was introduced after 4.1
 with the commit commit 785dbef407 ("KVM: s390: optimize round
 trip time in request handling"). After lots of cpu hotplugs in the
 guest (online/offline) sometimes a guest CPU did loop within host
 KVM code. Reason was that PROG_REQUEST was set in the sie control
 block, but no request was pending. This made commit 785dbef407
 the suspect and changing that area to always reset PROG_REQUEST
 did indeed fix the problem.
 
 Special thanks to David Hildenbrand, who helped understanding the
 exact sequence that led to the problem.
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Merge tag 'kvm-s390-master-20150730' of git://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into kvm-master

KVM: s390: bugfix for kvm/master (4.2)

Here is a bugfix for a regression that was introduced after 4.1
with the commit commit 785dbef407 ("KVM: s390: optimize round
trip time in request handling"). After lots of cpu hotplugs in the
guest (online/offline) sometimes a guest CPU did loop within host
KVM code. Reason was that PROG_REQUEST was set in the sie control
block, but no request was pending. This made commit 785dbef407
the suspect and changing that area to always reset PROG_REQUEST
did indeed fix the problem.

Special thanks to David Hildenbrand, who helped understanding the
exact sequence that led to the problem.
This commit is contained in:
Paolo Bonzini 2015-07-30 13:30:03 +02:00
commit 7307f70c6d
1 changed files with 2 additions and 2 deletions
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4
arch/s390/kvm/kvm-s390.c
View File

@ -1742,10 +1742,10 @@ static bool ibs_enabled(struct kvm_vcpu *vcpu)
static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
{
if (!vcpu->requests)
return 0;
retry:
kvm_s390_vcpu_request_handled(vcpu);
if (!vcpu->requests)
return 0;
/*
* We use MMU_RELOAD just to re-arm the ipte notifier for the
* guest prefix page. gmap_ipte_notify will wait on the ptl lock.