[PATCH RFC v2 10/11] KVM: s390: Add VSIE shadow configuration

[Christoph Schlameuss <schlameuss@linux.ibm.com>]

Introduce two new module parameters allowing to keep more shadow
structures

* vsie_shadow_scb_max
  Override the maximum number of VSIE control blocks / vsie_pages to
  shadow in guest-1. KVM will use the maximum of the current number of
  vCPUs and a maximum of 256 or this value if it is lower.
  This is the number of guest-3 control blocks / CPUs to keep shadowed
  to minimize the repeated shadowing effort.

* vsie_shadow_sca_max
  Override the maximum number of VSIE system control areas to
  shadow in guest-1. KVM will use a minimum of the current number of
  vCPUs and a maximum of 256 or this value if it is lower.
  This is the number of guest-3 system control areas / VMs to keep
  shadowed to minimize repeated shadowing effort.

Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
---
 arch/s390/kvm/vsie.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index b69ef763b55296875522f2e63169446b5e2d5053..cd114df5e119bd289d14037d1f1c5bfe148cf5c7 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -98,9 +98,19 @@ struct vsie_sca {
 	struct vsie_page	*pages[KVM_S390_MAX_VSIE_VCPUS];
 };
 
+/* maximum vsie shadow scb */
+unsigned int vsie_shadow_scb_max;
+module_param(vsie_shadow_scb_max, uint, 0644);
+MODULE_PARM_DESC(vsie_shadow_scb_max, "Maximum number of VSIE shadow control blocks to keep. Values smaller number vcpus uses number of vcpus; maximum 256");
+
+/* maximum vsie shadow sca */
+unsigned int vsie_shadow_sca_max;
+module_param(vsie_shadow_sca_max, uint, 0644);
+MODULE_PARM_DESC(vsie_shadow_sca_max, "Maximum number of VSIE shadow system control areas to keep. Values smaller number of vcpus uses number of vcpus; 0 to disable sca shadowing; maximum 256");
+
 static inline bool use_vsie_sigpif(struct kvm *kvm)
 {
-	return kvm->arch.use_vsie_sigpif;
+	return kvm->arch.use_vsie_sigpif && vsie_shadow_sca_max;
 }
 
 static inline bool use_vsie_sigpif_for(struct kvm *kvm, struct vsie_page *vsie_page)
@@ -907,7 +917,8 @@ static struct vsie_sca *get_vsie_sca(struct kvm_vcpu *vcpu, struct vsie_page *vs
 	 * We want at least #online_vcpus shadows, so every VCPU can execute the
 	 * VSIE in parallel. (Worst case all single core VMs.)
 	 */
-	max_sca = MIN(atomic_read(&kvm->online_vcpus), KVM_S390_MAX_VSIE_VCPUS);
+	max_sca = MIN(MAX(atomic_read(&kvm->online_vcpus), vsie_shadow_sca_max),
+		      KVM_S390_MAX_VSIE_VCPUS);
 	if (kvm->arch.vsie.sca_count < max_sca) {
 		BUILD_BUG_ON(sizeof(struct vsie_sca) > PAGE_SIZE);
 		sca_new = (void *)__get_free_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
@@ -1782,7 +1793,8 @@ static struct vsie_page *get_vsie_page(struct kvm_vcpu *vcpu, unsigned long addr
 		put_vsie_page(vsie_page);
 	}
 
-	max_vsie_page = MIN(atomic_read(&kvm->online_vcpus), KVM_S390_MAX_VSIE_VCPUS);
+	max_vsie_page = MIN(MAX(atomic_read(&kvm->online_vcpus), vsie_shadow_scb_max),
+			    KVM_S390_MAX_VSIE_VCPUS);
 
 	/* allocate new vsie_page - we will likely need it */
 	if (addr || kvm->arch.vsie.page_count < max_vsie_page) {

-- 
2.51.1