Subject: [PATCH v1 46/55] KVM: PPC: Book3S HV P9: Avoid tlbsync sequence on radix guest exit

From: Nicholas Piggin <[email-masked]>
Date: Mon, 26 Jul 2021 13:50:27 +1000

Use the existing TLB flushing logic to IPI the previous CPU and run the
necessary barriers before running a guest vCPU on a new physical CPU,
to do the necessary radix GTSE barriers for handling the case of an
interrupted guest tlbie sequence.

This results in more IPIs than the TLB flush logic requires, but it's
a significant win for common case scheduling when the vCPU remains on
the same physical CPU.

-522 cycles (5754) POWER9 virt-mode NULL hcall

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kvm/book3s_hv.c          | 31 +++++++++++++++++++++++----
 arch/powerpc/kvm/book3s_hv_p9_entry.c |  9 --------
 2 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index a37ab798eb7c..3e5c6b745394 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3005,6 +3005,25 @@ static void radix_flush_cpu(struct kvm *kvm, int cpu, struct kvm_vcpu *vcpu)
 			smp_call_function_single(i, do_nothing, NULL, 1);
 }
 
+static void do_migrate_away_vcpu(void *arg)
+{
+	struct kvm_vcpu *vcpu = arg;
+	struct kvm *kvm = vcpu->kvm;
+
+	/*
+	 * If the guest has GTSE, it may execute tlbie, so do a eieio; tlbsync;
+	 * ptesync sequence on the old CPU before migrating to a new one, in
+	 * case we interrupted the guest between a tlbie ; eieio ;
+	 * tlbsync; ptesync sequence.
+	 *
+	 * Otherwise, ptesync is sufficient.
+	 */
+	if (kvm->arch.lpcr & LPCR_GTSE)
+		asm volatile("eieio; tlbsync; ptesync");
+	else
+		asm volatile("ptesync");
+}
+
 static void kvmppc_prepare_radix_vcpu(struct kvm_vcpu *vcpu, int pcpu)
 {
 	struct kvm_nested_guest *nested = vcpu->arch.nested;
@@ -3032,10 +3051,14 @@ static void kvmppc_prepare_radix_vcpu(struct kvm_vcpu *vcpu, int pcpu)
 	 * so we use a single bit in .need_tlb_flush for all 4 threads.
 	 */
 	if (prev_cpu != pcpu) {
-		if (prev_cpu >= 0 &&
-		    cpu_first_tlb_thread_sibling(prev_cpu) !=
-		    cpu_first_tlb_thread_sibling(pcpu))
-			radix_flush_cpu(kvm, prev_cpu, vcpu);
+		if (prev_cpu >= 0) {
+			if (cpu_first_tlb_thread_sibling(prev_cpu) !=
+			    cpu_first_tlb_thread_sibling(pcpu))
+				radix_flush_cpu(kvm, prev_cpu, vcpu);
+
+			smp_call_function_single(prev_cpu,
+					do_migrate_away_vcpu, vcpu, 1);
+		}
 		if (nested)
 			nested->prev_cpu[vcpu->arch.nested_vcpu_id] = pcpu;
 		else
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index 52690af66ca9..1bb81be09d4f 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -1039,15 +1039,6 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
 	local_paca->kvm_hstate.in_guest = KVM_GUEST_MODE_NONE;
 
-	if (kvm_is_radix(kvm)) {
-		/*
-		 * Since this is radix, do a eieio; tlbsync; ptesync sequence
-		 * in case we interrupted the guest between a tlbie and a
-		 * ptesync.
-		 */
-		asm volatile("eieio; tlbsync; ptesync");
-	}
-
 	/*
 	 * cp_abort is required if the processor supports local copy-paste
 	 * to clear the copy buffer that was under control of the guest.
-- 
2.23.0