[PATCH 14/23] KVM: PPC: Book3S PR: Delay disabling relocation-on interrupts

[Paul Mackerras <paulus@samba.org>]

When we are running a PR KVM guest on POWER8, we have to disable the
new POWER8 feature of taking interrupts with relocation on, that is,
of taking interrupts without disabling the MMU, because the SLB does
not contain the normal kernel SLB entries while in the guest.
Currently we disable relocation-on interrupts when a PR guest is
created, and leave it disabled until there are no more PR guests in
existence.

This defers the disabling of relocation-on interrupts until the first
time a PR KVM guest vcpu is run.  The reason is that in future we will
support both PR and HV guests in the same kernel, and this will avoid
disabling relocation-on interrupts unnecessarily for guests which turn
out to be HV guests, as we will not know at VM creation time whether
it will be a PR or a HV guest.

Signed-off-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/kvm_host.h |  1 +
 arch/powerpc/kvm/book3s_pr.c        | 71 ++++++++++++++++++++++++++-----------
 2 files changed, 52 insertions(+), 20 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 4d83972..c012db2 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -264,6 +264,7 @@ struct kvm_arch {
 #endif /* CONFIG_KVM_BOOK3S_64_HV */
 #ifdef CONFIG_KVM_BOOK3S_PR
 	struct mutex hpt_mutex;
+	bool relon_disabled;
 #endif
 #ifdef CONFIG_PPC_BOOK3S_64
 	struct list_head spapr_tce_tables;
diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 5b06a70..2759ddc 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -1197,6 +1197,47 @@ void kvmppc_core_vcpu_free(struct kvm_vcpu *vcpu)
 	kmem_cache_free(kvm_vcpu_cache, vcpu);
 }
 
+/*
+ * On POWER8, we have to disable relocation-on interrupts while
+ * we are in the guest, since the guest doesn't have the normal
+ * kernel SLB contents.  Since disabling relocation-on interrupts
+ * is a fairly heavy-weight operation, we do it once when starting
+ * the first guest vcpu and leave it disabled until the last guest
+ * has been destroyed.
+ */
+static unsigned int kvm_global_user_count = 0;
+static DEFINE_SPINLOCK(kvm_global_user_count_lock);
+
+static void disable_relon_interrupts(struct kvm *kvm)
+{
+	mutex_lock(&kvm->lock);
+	if (!kvm->arch.relon_disabled) {
+		if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
+			spin_lock(&kvm_global_user_count_lock);
+			if (++kvm_global_user_count == 1)
+				pSeries_disable_reloc_on_exc();
+			spin_unlock(&kvm_global_user_count_lock);
+		}
+		/* order disabling above with setting relon_disabled */
+		smp_mb();
+		kvm->arch.relon_disabled = true;
+	}
+	mutex_unlock(&kvm->lock);
+}
+
+static void enable_relon_interrupts(struct kvm *kvm)
+{
+	if (kvm->arch.relon_disabled &&
+	    firmware_has_feature(FW_FEATURE_SET_MODE)) {
+		spin_lock(&kvm_global_user_count_lock);
+		BUG_ON(kvm_global_user_count == 0);
+		if (--kvm_global_user_count == 0)
+			pSeries_enable_reloc_on_exc();
+		spin_unlock(&kvm_global_user_count_lock);
+	}
+	kvm->arch.relon_disabled = false;
+}
+
 int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 {
 	int ret;
@@ -1234,6 +1275,9 @@ int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 		goto out;
 	}
 
+	if (!vcpu->kvm->arch.relon_disabled)
+		disable_relon_interrupts(vcpu->kvm);
+
 	/* Save FPU state in stack */
 	if (current->thread.regs->msr & MSR_FP)
 		giveup_fpu(current);
@@ -1400,9 +1444,6 @@ void kvmppc_core_flush_memslot(struct kvm *kvm, struct kvm_memory_slot *memslot)
 {
 }
 
-static unsigned int kvm_global_user_count = 0;
-static DEFINE_SPINLOCK(kvm_global_user_count_lock);
-
 int kvmppc_core_init_vm(struct kvm *kvm)
 {
 #ifdef CONFIG_PPC64
@@ -1411,28 +1452,18 @@ int kvmppc_core_init_vm(struct kvm *kvm)
 #endif
 	mutex_init(&kvm->arch.hpt_mutex);
 
-	if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
-		spin_lock(&kvm_global_user_count_lock);
-		if (++kvm_global_user_count == 1)
-			pSeries_disable_reloc_on_exc();
-		spin_unlock(&kvm_global_user_count_lock);
-	}
+	/*
+	 * If we don't have relocation-on interrupts at all,
+	 * then we can consider them to be already disabled.
+	 */
+	kvm->arch.relon_disabled = !firmware_has_feature(FW_FEATURE_SET_MODE);
+
 	return 0;
 }
 
 void kvmppc_core_destroy_vm(struct kvm *kvm)
 {
-#ifdef CONFIG_PPC64
-	WARN_ON(!list_empty(&kvm->arch.spapr_tce_tables));
-#endif
-
-	if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
-		spin_lock(&kvm_global_user_count_lock);
-		BUG_ON(kvm_global_user_count == 0);
-		if (--kvm_global_user_count == 0)
-			pSeries_enable_reloc_on_exc();
-		spin_unlock(&kvm_global_user_count_lock);
-	}
+	enable_relon_interrupts(kvm);
 }
 
 static int kvmppc_book3s_init(void)
-- 
1.8.3.1