* Document the interaction between KVM_CAP_HALT_POLL and halt_poll_ns

* s390: fix multi-epoch extension in nested guests
 
 * x86: fix uninitialized variable on nested triple fault
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Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

Pull kvm fixes from Paolo Bonzini:
 "Unless anything comes from the ARM side, this should be the last pull
  request for this release - and it's mostly documentation:

   - Document the interaction between KVM_CAP_HALT_POLL and halt_poll_ns

   - s390: fix multi-epoch extension in nested guests

   - x86: fix uninitialized variable on nested triple fault"

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  KVM: Document the interaction between KVM_CAP_HALT_POLL and halt_poll_ns
  KVM: Move halt-polling documentation into common directory
  KVM: x86: fix uninitialized variable use on KVM_REQ_TRIPLE_FAULT
  KVM: s390: vsie: Fix the initialization of the epoch extension (epdx) field

Documentation/virt/kvm/api.rst

@@ -7213,14 +7213,13 @@ veto the transition.
 :Parameters: args[0] is the maximum poll time in nanoseconds
 :Returns: 0 on success; -1 on error
 
-This capability overrides the kvm module parameter halt_poll_ns for the
-target VM.
+KVM_CAP_HALT_POLL overrides the kvm.halt_poll_ns module parameter to set the
+maximum halt-polling time for all vCPUs in the target VM. This capability can
+be invoked at any time and any number of times to dynamically change the
+maximum halt-polling time.
 
-VCPU polling allows a VCPU to poll for wakeup events instead of immediately
-scheduling during guest halts. The maximum time a VCPU can spend polling is
-controlled by the kvm module parameter halt_poll_ns. This capability allows
-the maximum halt time to specified on a per-VM basis, effectively overriding
-the module parameter for the target VM.
+See Documentation/virt/kvm/halt-polling.rst for more information on halt
+polling.
 
 7.21 KVM_CAP_X86_USER_SPACE_MSR
 -------------------------------

Documentation/virt/kvm/halt-polling.rst

@@ -119,6 +119,19 @@ These module parameters can be set from the debugfs files in:
 Note: that these module parameters are system wide values and are not able to
       be tuned on a per vm basis.
 
+Any changes to these parameters will be picked up by new and existing vCPUs the
+next time they halt, with the notable exception of VMs using KVM_CAP_HALT_POLL
+(see next section).
+
+KVM_CAP_HALT_POLL
+=================
+
+KVM_CAP_HALT_POLL is a VM capability that allows userspace to override halt_poll_ns
+on a per-VM basis. VMs using KVM_CAP_HALT_POLL ignore halt_poll_ns completely (but
+still obey halt_poll_ns_grow, halt_poll_ns_grow_start, and halt_poll_ns_shrink).
+
+See Documentation/virt/kvm/api.rst for more information on this capability.
+
 Further Notes
 =============
 

Documentation/virt/kvm/index.rst

@@ -17,4 +17,5 @@ KVM
 
    locking
    vcpu-requests
+   halt-polling
    review-checklist

Documentation/virt/kvm/x86/index.rst

@@ -10,7 +10,6 @@ KVM for x86 systems
    amd-memory-encryption
    cpuid
    errata
-   halt-polling
    hypercalls
    mmu
    msr

arch/s390/kvm/vsie.c

@@ -546,8 +546,10 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 	if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_CEI))
 		scb_s->eca |= scb_o->eca & ECA_CEI;
 	/* Epoch Extension */
-	if (test_kvm_facility(vcpu->kvm, 139))
+	if (test_kvm_facility(vcpu->kvm, 139)) {
 		scb_s->ecd |= scb_o->ecd & ECD_MEF;
+		scb_s->epdx = scb_o->epdx;
+	}
 
 	/* etoken */
 	if (test_kvm_facility(vcpu->kvm, 156))

arch/x86/kvm/x86.c

@@ -10574,9 +10574,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 				vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
 				vcpu->mmio_needed = 0;
 				r = 0;
-			}
 				goto out;
 			}
+		}
 		if (kvm_check_request(KVM_REQ_APF_HALT, vcpu)) {
 			/* Page is swapped out. Do synthetic halt */
 			vcpu->arch.apf.halted = true;