From 87e28a15c42cc592009c32a8c20e5789059027c2 Mon Sep 17 00:00:00 2001 From: Pierre Morel Date: Mon, 7 Sep 2020 15:26:07 +0200 Subject: 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 Link: https://lore.kernel.org/r/1613997661-22525-2-git-send-email-pmorel@linux.ibm.com Reviewed-by: Cornelia Huck Signed-off-by: Christian Borntraeger --- arch/s390/kvm/diag.c | 31 ++++++++++++++++++++++++++++--- arch/s390/kvm/kvm-s390.c | 6 ++++++ arch/s390/kvm/kvm-s390.h | 8 ++++++++ 3 files changed, 42 insertions(+), 3 deletions(-) (limited to 'arch/s390/kvm') 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; diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 333193982e51..cfe720d16a6a 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -158,6 +158,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = { VCPU_STAT("instruction_diag_44", diagnose_44), VCPU_STAT("instruction_diag_9c", diagnose_9c), VCPU_STAT("diag_9c_ignored", diagnose_9c_ignored), + VCPU_STAT("diag_9c_forward", diagnose_9c_forward), VCPU_STAT("instruction_diag_258", diagnose_258), VCPU_STAT("instruction_diag_308", diagnose_308), VCPU_STAT("instruction_diag_500", diagnose_500), @@ -185,6 +186,11 @@ static bool use_gisa = true; module_param(use_gisa, bool, 0644); MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it."); +/* maximum diag9c forwarding per second */ +unsigned int diag9c_forwarding_hz; +module_param(diag9c_forwarding_hz, uint, 0644); +MODULE_PARM_DESC(diag9c_forwarding_hz, "Maximum diag9c forwarding per second, 0 to turn off"); + /* * For now we handle at most 16 double words as this is what the s390 base * kernel handles and stores in the prefix page. If we ever need to go beyond diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h index 79dcd647b378..9fad25109b0d 100644 --- a/arch/s390/kvm/kvm-s390.h +++ b/arch/s390/kvm/kvm-s390.h @@ -471,4 +471,12 @@ void kvm_s390_reinject_machine_check(struct kvm_vcpu *vcpu, * @kvm: the KVM guest */ void kvm_s390_vcpu_crypto_reset_all(struct kvm *kvm); + +/** + * diag9c_forwarding_hz + * + * Set the maximum number of diag9c forwarding per second + */ +extern unsigned int diag9c_forwarding_hz; + #endif -- cgit v1.2.3