KVM: PPC: Book3E: Increase FPU laziness

Increase FPU laziness by loading the guest state into the unit before entering
the guest instead of doing it on each vcpu schedule. Without this improvement
an interrupt may claim floating point corrupting guest state.

Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 36 insertions, 7 deletions

diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index 074b7fc795b7..91e7217db9d9 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -124,6 +124,40 @@ static void kvmppc_vcpu_sync_spe(struct kvm_vcpu *vcpu)
 }
 #endif
 
+/*
+ * Load up guest vcpu FP state if it's needed.
+ * It also set the MSR_FP in thread so that host know
+ * we're holding FPU, and then host can help to save
+ * guest vcpu FP state if other threads require to use FPU.
+ * This simulates an FP unavailable fault.
+ *
+ * It requires to be called with preemption disabled.
+ */
+static inline void kvmppc_load_guest_fp(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_PPC_FPU
+	if (!(current->thread.regs->msr & MSR_FP)) {
+		enable_kernel_fp();
+		load_fp_state(&vcpu->arch.fp);
+		current->thread.fp_save_area = &vcpu->arch.fp;
+		current->thread.regs->msr |= MSR_FP;
+	}
+#endif
+}
+
+/*
+ * Save guest vcpu FP state into thread.
+ * It requires to be called with preemption disabled.
+ */
+static inline void kvmppc_save_guest_fp(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_PPC_FPU
+	if (current->thread.regs->msr & MSR_FP)
+		giveup_fpu(current);
+	current->thread.fp_save_area = NULL;
+#endif
+}
+
 static void kvmppc_vcpu_sync_fpu(struct kvm_vcpu *vcpu)
 {
 #if defined(CONFIG_PPC_FPU) && !defined(CONFIG_KVM_BOOKE_HV)
@@ -658,12 +692,8 @@ int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 
 	/*
 	 * Since we can't trap on MSR_FP in GS-mode, we consider the guest
-	 * as always using the FPU.  Kernel usage of FP (via
-	 * enable_kernel_fp()) in this thread must not occur while
-	 * vcpu->fpu_active is set.
+	 * as always using the FPU.
 	 */
-	vcpu->fpu_active = 1;
-
 	kvmppc_load_guest_fp(vcpu);
 #endif
 
@@ -687,8 +717,6 @@ int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 
 #ifdef CONFIG_PPC_FPU
 	kvmppc_save_guest_fp(vcpu);
-
-	vcpu->fpu_active = 0;
 #endif
 
 out:
@@ -1194,6 +1222,7 @@ out:
 		else {
 			/* interrupts now hard-disabled */
 			kvmppc_fix_ee_before_entry();
+			kvmppc_load_guest_fp(vcpu);
 		}
 	}