[PATCH 2/7] KVM: Add a @force param to __kvm_vcpu_kick() for PPC backwards compatibility

[Sean Christopherson]

Plumb in a @force param to __kvm_vcpu_kick() to force an IPI without
checking kvm_arch_vcpu_should_kick().  The param will be used to drop
kvm_arch_vcpu_should_kick() in favor of kvm_request_needs_ipi() without
regressing PPC, which for unknown reasons unconditionally blasts an IPI
in a variety of kvm_vcpu_kick() flows.

No functional change intended (nothing yet passes in @force=true).

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 include/linux/kvm_host.h |  6 +++---
 virt/kvm/kvm_main.c      | 10 +++++++---
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e7fc94e2910a..3b9844c3906d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1570,11 +1570,11 @@ void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu);
 bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu);
 
 #ifndef CONFIG_S390
-void __kvm_vcpu_kick(struct kvm_vcpu *vcpu, bool wait);
+void __kvm_vcpu_kick(struct kvm_vcpu *vcpu, bool wait, bool force);
 
 static inline void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
 {
-	__kvm_vcpu_kick(vcpu, false);
+	__kvm_vcpu_kick(vcpu, false, false);
 }
 #endif
 
@@ -2315,7 +2315,7 @@ static __always_inline void kvm_make_request(int req, struct kvm_vcpu *vcpu)
 static inline void kvm_make_request_and_kick(int req, struct kvm_vcpu *vcpu)
 {
 	kvm_make_request(req, vcpu);
-	__kvm_vcpu_kick(vcpu, req & KVM_REQUEST_WAIT);
+	__kvm_vcpu_kick(vcpu, req & KVM_REQUEST_WAIT, false);
 }
 #endif
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index cf4cb586f140..67addb9e48a7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3908,7 +3908,7 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_vcpu_wake_up);
 /*
  * Kick a sleeping VCPU, or a guest VCPU in guest mode, into host kernel mode.
  */
-void __kvm_vcpu_kick(struct kvm_vcpu *vcpu, bool wait)
+void __kvm_vcpu_kick(struct kvm_vcpu *vcpu, bool wait, bool force)
 {
 	int me, cpu;
 
@@ -3933,9 +3933,13 @@ void __kvm_vcpu_kick(struct kvm_vcpu *vcpu, bool wait)
 	 * after kvm_arch_vcpu_should_kick(), which could result in sending an
 	 * IPI to the previous pCPU.  But, that's ok because the purpose of the
 	 * IPI is to force the vCPU to leave IN_GUEST_MODE, and migrating the
-	 * vCPU also requires it to leave IN_GUEST_MODE.
+	 * vCPU also requires it to leave IN_GUEST_MODE
+	 *
+	 * Note #2, do NOT check if an IPI is needed if @force is true, as the
+	 * check also modifies vcpu->mode and KVM PPC needs to avoid that side
+	 * effect for unknown historical reasons.
 	 */
-	if (kvm_arch_vcpu_should_kick(vcpu)) {
+	if (force || kvm_arch_vcpu_should_kick(vcpu)) {
 		cpu = READ_ONCE(vcpu->cpu);
 		if (cpu != me && (unsigned int)cpu < nr_cpu_ids && cpu_online(cpu)) {
 			/*
-- 
2.56.0.313.g2479322e68-goog