[RFC PATCH 5/6] KVM: PPC: Book3S HV P9: Stop using vc->dpdes

[Nicholas Piggin]

The P9 path uses vc->dpdes only for msgsndp / SMT emulation. This adds
an ordering requirement between vcpu->doorbell_request and vc->dpdes for
no real benefit. Use vcpu->doorbell_request directly.

XXX: verify msgsndp / DPDES emulation works properly.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/kvm/book3s_hv.c          | 18 ++++++++++--------
 arch/powerpc/kvm/book3s_hv_builtin.c  |  2 ++
 arch/powerpc/kvm/book3s_hv_p9_entry.c | 14 ++++++++++----
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 93ecbc040529..957efde59014 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -766,6 +766,8 @@ static bool kvmppc_doorbell_pending(struct kvm_vcpu *vcpu)
 
 	if (vcpu->arch.doorbell_request)
 		return true;
+	if (cpu_has_feature(CPU_FTR_ARCH_300))
+		return false;
 	/*
 	 * Ensure that the read of vcore->dpdes comes after the read
 	 * of vcpu->doorbell_request.  This barrier matches the
@@ -2165,8 +2167,10 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 		 * either vcore->dpdes or doorbell_request.
 		 * On POWER8, doorbell_request is 0.
 		 */
-		*val = get_reg_val(id, vcpu->arch.vcore->dpdes |
-				   vcpu->arch.doorbell_request);
+		if (cpu_has_feature(CPU_FTR_ARCH_300))
+			*val = get_reg_val(id, vcpu->arch.doorbell_request);
+		else
+			*val = get_reg_val(id, vcpu->arch.vcore->dpdes);
 		break;
 	case KVM_REG_PPC_VTB:
 		*val = get_reg_val(id, vcpu->arch.vcore->vtb);
@@ -2403,7 +2407,10 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 		vcpu->arch.pspb = set_reg_val(id, *val);
 		break;
 	case KVM_REG_PPC_DPDES:
-		vcpu->arch.vcore->dpdes = set_reg_val(id, *val);
+		if (cpu_has_feature(CPU_FTR_ARCH_300))
+			vcpu->arch.doorbell_request = set_reg_val(id, *val) & 1;
+		else
+			vcpu->arch.vcore->dpdes = set_reg_val(id, *val);
 		break;
 	case KVM_REG_PPC_VTB:
 		vcpu->arch.vcore->vtb = set_reg_val(id, *val);
@@ -4431,11 +4438,6 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
 
 	if (!nested) {
 		kvmppc_core_prepare_to_enter(vcpu);
-		if (vcpu->arch.doorbell_request) {
-			vc->dpdes = 1;
-			smp_wmb();
-			vcpu->arch.doorbell_request = 0;
-		}
 		if (test_bit(BOOK3S_IRQPRIO_EXTERNAL,
 			     &vcpu->arch.pending_exceptions))
 			lpcr |= LPCR_MER;
diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c
index be8ef1c5b1bf..9d24f4472b42 100644
--- a/arch/powerpc/kvm/book3s_hv_builtin.c
+++ b/arch/powerpc/kvm/book3s_hv_builtin.c
@@ -649,6 +649,8 @@ void kvmppc_guest_entry_inject_int(struct kvm_vcpu *vcpu)
 	int ext;
 	unsigned long lpcr;
 
+	WARN_ON_ONCE(cpu_has_feature(CPU_FTR_ARCH_300));
+
 	/* Insert EXTERNAL bit into LPCR at the MER bit position */
 	ext = (vcpu->arch.pending_exceptions >> BOOK3S_IRQPRIO_EXTERNAL) & 1;
 	lpcr = mfspr(SPRN_LPCR);
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index 82dac23cc678..44150a29f6e0 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -677,6 +677,7 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	unsigned long host_pidr;
 	unsigned long host_dawr1;
 	unsigned long host_dawrx1;
+	unsigned long dpdes;
 
 	hdec = time_limit - *tb;
 	if (hdec < 0)
@@ -736,8 +737,10 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
 	if (vc->pcr)
 		mtspr(SPRN_PCR, vc->pcr | PCR_MASK);
-	if (vc->dpdes)
-		mtspr(SPRN_DPDES, vc->dpdes);
+	if (vcpu->arch.doorbell_request) {
+		vcpu->arch.doorbell_request = 0;
+		mtspr(SPRN_DPDES, 1);
+	}
 
 	if (dawr_enabled()) {
 		if (vcpu->arch.dawr0 != host_dawr0)
@@ -968,7 +971,10 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	vcpu->arch.shregs.sprg2 = mfspr(SPRN_SPRG2);
 	vcpu->arch.shregs.sprg3 = mfspr(SPRN_SPRG3);
 
-	vc->dpdes = mfspr(SPRN_DPDES);
+	dpdes = mfspr(SPRN_DPDES);
+	if (dpdes)
+		vcpu->arch.doorbell_request = 1;
+
 	vc->vtb = mfspr(SPRN_VTB);
 
 	dec = mfspr(SPRN_DEC);
@@ -1030,7 +1036,7 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 		}
 	}
 
-	if (vc->dpdes)
+	if (dpdes)
 		mtspr(SPRN_DPDES, 0);
 	if (vc->pcr)
 		mtspr(SPRN_PCR, PCR_MASK);
-- 
2.23.0