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| author | Pierre Morel <pmorel@linux.ibm.com> | 2020-09-07 15:26:07 +0200 |
|---|---|---|
| committer | Christian Borntraeger <borntraeger@de.ibm.com> | 2021-03-09 10:16:26 +0100 |
| commit | 87e28a15c42cc592009c32a8c20e5789059027c2 (patch) | |
| tree | d1fecf787809e547737239ce637072fcca473c18 /arch/s390/kvm/diag.c | |
| parent | 38860756a19042c2159178f57ec6e147b13ddfc2 (diff) | |
| download | linux-87e28a15c42cc592009c32a8c20e5789059027c2.tar.gz linux-87e28a15c42cc592009c32a8c20e5789059027c2.tar.bz2 linux-87e28a15c42cc592009c32a8c20e5789059027c2.zip | |
KVM: s390: diag9c (directed yield) forwarding
When we intercept a DIAG_9C from the guest we verify that the
target real CPU associated with the virtual CPU designated by
the guest is running and if not we forward the DIAG_9C to the
target real CPU.
To avoid a diag9c storm we allow a maximal rate of diag9c forwarding.
The rate is calculated as a count per second defined as a new
parameter of the s390 kvm module: diag9c_forwarding_hz .
The default value of 0 is to not forward diag9c.
Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Link: https://lore.kernel.org/r/1613997661-22525-2-git-send-email-pmorel@linux.ibm.com
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Diffstat (limited to 'arch/s390/kvm/diag.c')
| -rw-r--r-- | arch/s390/kvm/diag.c | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c index 5b8ec1c447e1..02c146f9e5cd 100644 --- a/arch/s390/kvm/diag.c +++ b/arch/s390/kvm/diag.c @@ -150,6 +150,19 @@ static int __diag_time_slice_end(struct kvm_vcpu *vcpu) return 0; } +static int forward_cnt; +static unsigned long cur_slice; + +static int diag9c_forwarding_overrun(void) +{ + /* Reset the count on a new slice */ + if (time_after(jiffies, cur_slice)) { + cur_slice = jiffies; + forward_cnt = diag9c_forwarding_hz / HZ; + } + return forward_cnt-- <= 0 ? 1 : 0; +} + static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) { struct kvm_vcpu *tcpu; @@ -167,9 +180,21 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu) if (!tcpu) goto no_yield; - /* target already running */ - if (READ_ONCE(tcpu->cpu) >= 0) - goto no_yield; + /* target guest VCPU already running */ + if (READ_ONCE(tcpu->cpu) >= 0) { + if (!diag9c_forwarding_hz || diag9c_forwarding_overrun()) + goto no_yield; + + /* target host CPU already running */ + if (!vcpu_is_preempted(tcpu->cpu)) + goto no_yield; + smp_yield_cpu(tcpu->cpu); + VCPU_EVENT(vcpu, 5, + "diag time slice end directed to %d: yield forwarded", + tid); + vcpu->stat.diagnose_9c_forward++; + return 0; + } if (kvm_vcpu_yield_to(tcpu) <= 0) goto no_yield; |