[RFC PATCH 18/43] KVM: PPC: Book3S HV P9: Improve mtmsrd scheduling by delaying MSR[EE] disable

[Nicholas Piggin <npiggin@gmail.com>]

Moving the mtmsrd after the host SPRs are saved and before the guest
SPRs start to be loaded can prevent an SPR scoreboard stall (because
the mtmsrd is L=1 type which does not cause context synchronisation.

This is also now more convenient to combined with the mtmsrd L=0
instruction to enable facilities just below, but that is not done yet.

-12 cycles (7791) POWER9 virt-mode NULL hcall

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kvm/book3s_hv.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 3ac5dbdb59f8..b8b0695a9312 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4015,6 +4015,18 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
 
 	save_p9_host_os_sprs(&host_os_sprs);
 
+	/*
+	 * This could be combined with MSR[RI] clearing, but that expands
+	 * the unrecoverable window. It would be better to cover unrecoverable
+	 * with KVM bad interrupt handling rather than use MSR[RI] at all.
+	 *
+	 * Much more difficult and less worthwhile to combine with IR/DR
+	 * disable.
+	 */
+	hard_irq_disable();
+	if (lazy_irq_pending())
+		return 0;
+
 	/* MSR bits may have been cleared by context switch */
 	msr = 0;
 	if (IS_ENABLED(CONFIG_PPC_FPU))
@@ -4512,6 +4524,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
 	struct kvmppc_vcore *vc;
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_nested_guest *nested = vcpu->arch.nested;
+	unsigned long flags;
 
 	trace_kvmppc_run_vcpu_enter(vcpu);
 
@@ -4555,11 +4568,11 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
 	if (kvm_is_radix(kvm))
 		kvmppc_prepare_radix_vcpu(vcpu, pcpu);
 
-	local_irq_disable();
-	hard_irq_disable();
+	/* flags save not required, but irq_pmu has no disable/enable API */
+	powerpc_local_irq_pmu_save(flags);
 	if (signal_pending(current))
 		goto sigpend;
-	if (lazy_irq_pending() || need_resched() || !kvm->arch.mmu_ready)
+	if (need_resched() || !kvm->arch.mmu_ready)
 		goto out;
 
 	if (!nested) {
@@ -4614,7 +4627,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
 
 	guest_exit_irqoff();
 
-	local_irq_enable();
+	powerpc_local_irq_pmu_restore(flags);
 
 	cpumask_clear_cpu(pcpu, &kvm->arch.cpu_in_guest);
 
@@ -4672,7 +4685,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
 	run->exit_reason = KVM_EXIT_INTR;
 	vcpu->arch.ret = -EINTR;
  out:
-	local_irq_enable();
+	powerpc_local_irq_pmu_restore(flags);
 	preempt_enable();
 	goto done;
 }
-- 
2.23.0