KVM: PPC: Book3S HV P9: Don't restore PSSCR if not needed

This also moves the PSSCR update in nested entry to avoid a SPR
scoreboard stall.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-42-npiggin@gmail.com

arch/powerpc/kvm/book3s_hv.c

@@ -3889,7 +3889,9 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu *vcpu, u64 time_limit, uns
 	if (unlikely(load_vcpu_state(vcpu, &host_os_sprs)))
 		msr = mfmsr(); /* TM restore can update msr */
 
-	mtspr(SPRN_PSSCR_PR, vcpu->arch.psscr);
+	if (vcpu->arch.psscr != host_psscr)
+		mtspr(SPRN_PSSCR_PR, vcpu->arch.psscr);
+
 	kvmhv_save_hv_regs(vcpu, &hvregs);
 	hvregs.lpcr = lpcr;
 	vcpu->arch.regs.msr = vcpu->arch.shregs.msr;
@@ -3930,7 +3932,6 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu *vcpu, u64 time_limit, uns
 	vcpu->arch.shregs.dar = mfspr(SPRN_DAR);
 	vcpu->arch.shregs.dsisr = mfspr(SPRN_DSISR);
 	vcpu->arch.psscr = mfspr(SPRN_PSSCR_PR);
-	mtspr(SPRN_PSSCR_PR, host_psscr);
 
 	store_vcpu_state(vcpu);
 
@@ -3943,6 +3944,8 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu *vcpu, u64 time_limit, uns
 	timer_rearm_host_dec(*tb);
 
 	restore_p9_host_os_sprs(vcpu, &host_os_sprs);
+	if (vcpu->arch.psscr != host_psscr)
+		mtspr(SPRN_PSSCR_PR, host_psscr);
 
 	return trap;
 }

arch/powerpc/kvm/book3s_hv_p9_entry.c

@@ -649,6 +649,7 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	unsigned long host_dawr0;
 	unsigned long host_dawrx0;
 	unsigned long host_psscr;
+	unsigned long host_hpsscr;
 	unsigned long host_pidr;
 	unsigned long host_dawr1;
 	unsigned long host_dawrx1;
@@ -666,7 +667,9 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
 	host_hfscr = mfspr(SPRN_HFSCR);
 	host_ciabr = mfspr(SPRN_CIABR);
-	host_psscr = mfspr(SPRN_PSSCR);
+	host_psscr = mfspr(SPRN_PSSCR_PR);
+	if (cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+		host_hpsscr = mfspr(SPRN_PSSCR);
 	host_pidr = mfspr(SPRN_PID);
 
 	if (dawr_enabled()) {
@@ -750,8 +753,14 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	if (vcpu->arch.ciabr != host_ciabr)
 		mtspr(SPRN_CIABR, vcpu->arch.ciabr);
 
-	mtspr(SPRN_PSSCR, vcpu->arch.psscr | PSSCR_EC |
-	      (local_paca->kvm_hstate.fake_suspend << PSSCR_FAKE_SUSPEND_LG));
+
+	if (cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) {
+		mtspr(SPRN_PSSCR, vcpu->arch.psscr | PSSCR_EC |
+		      (local_paca->kvm_hstate.fake_suspend << PSSCR_FAKE_SUSPEND_LG));
+	} else {
+		if (vcpu->arch.psscr != host_psscr)
+			mtspr(SPRN_PSSCR_PR, vcpu->arch.psscr);
+	}
 
 	mtspr(SPRN_HFSCR, vcpu->arch.hfscr);
 
@@ -957,7 +966,7 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
 	vcpu->arch.ic = mfspr(SPRN_IC);
 	vcpu->arch.pid = mfspr(SPRN_PID);
-	vcpu->arch.psscr = mfspr(SPRN_PSSCR) & PSSCR_GUEST_VIS;
+	vcpu->arch.psscr = mfspr(SPRN_PSSCR_PR);
 
 	vcpu->arch.shregs.sprg0 = mfspr(SPRN_SPRG0);
 	vcpu->arch.shregs.sprg1 = mfspr(SPRN_SPRG1);
@@ -1003,9 +1012,12 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	mtspr(SPRN_PURR, local_paca->kvm_hstate.host_purr);
 	mtspr(SPRN_SPURR, local_paca->kvm_hstate.host_spurr);
 
-	/* Preserve PSSCR[FAKE_SUSPEND] until we've called kvmppc_save_tm_hv */
-	mtspr(SPRN_PSSCR, host_psscr |
-	      (local_paca->kvm_hstate.fake_suspend << PSSCR_FAKE_SUSPEND_LG));
+	if (cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) {
+		/* Preserve PSSCR[FAKE_SUSPEND] until we've called kvmppc_save_tm_hv */
+		mtspr(SPRN_PSSCR, host_hpsscr |
+		      (local_paca->kvm_hstate.fake_suspend << PSSCR_FAKE_SUSPEND_LG));
+	}
+
 	mtspr(SPRN_HFSCR, host_hfscr);
 	if (vcpu->arch.ciabr != host_ciabr)
 		mtspr(SPRN_CIABR, host_ciabr);