KVM: PPC: Book3S HV P9: Demand fault TM facility registers

Use HFSCR facility disabling to implement demand faulting for TM, with
a hysteresis counter similar to the load_fp etc counters in context
switching that implement the equivalent demand faulting for userspace
facilities.

This speeds up guest entry/exit by avoiding the register save/restore
when a guest is not frequently using them. When a guest does use them
often, there will be some additional demand fault overhead, but these
are not commonly used facilities.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-38-npiggin@gmail.com

arch/powerpc/include/asm/kvm_host.h

@@ -580,6 +580,9 @@ struct kvm_vcpu_arch {
 	ulong ppr;
 	u32 pspb;
 	u8 load_ebb;
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+	u8 load_tm;
+#endif
 	ulong fscr;
 	ulong shadow_fscr;
 	ulong ebbhr;

arch/powerpc/kvm/book3s_hv.c

@@ -1446,6 +1446,16 @@ static int kvmppc_ebb_unavailable(struct kvm_vcpu *vcpu)
 	return RESUME_GUEST;
 }
 
+static int kvmppc_tm_unavailable(struct kvm_vcpu *vcpu)
+{
+	if (!(vcpu->arch.hfscr_permitted & HFSCR_TM))
+		return EMULATE_FAIL;
+
+	vcpu->arch.hfscr |= HFSCR_TM;
+
+	return RESUME_GUEST;
+}
+
 static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
 				 struct task_struct *tsk)
 {
@@ -1739,6 +1749,8 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
 				r = kvmppc_pmu_unavailable(vcpu);
 			if (cause == FSCR_EBB_LG)
 				r = kvmppc_ebb_unavailable(vcpu);
+			if (cause == FSCR_TM_LG)
+				r = kvmppc_tm_unavailable(vcpu);
 		}
 		if (r == EMULATE_FAIL) {
 			kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
@@ -2783,9 +2795,9 @@ static int kvmppc_core_vcpu_create_hv(struct kvm_vcpu *vcpu)
 	vcpu->arch.hfscr_permitted = vcpu->arch.hfscr;
 
 	/*
-	 * PM, EBB is demand-faulted so start with it clear.
+	 * PM, EBB, TM are demand-faulted so start with it clear.
 	 */
-	vcpu->arch.hfscr &= ~(HFSCR_PM | HFSCR_EBB);
+	vcpu->arch.hfscr &= ~(HFSCR_PM | HFSCR_EBB | HFSCR_TM);
 
 	kvmppc_mmu_book3s_hv_init(vcpu);
 
@@ -3868,8 +3880,9 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu *vcpu, u64 time_limit, uns
 		msr |= MSR_VEC;
 	if (cpu_has_feature(CPU_FTR_VSX))
 		msr |= MSR_VSX;
-	if (cpu_has_feature(CPU_FTR_TM) ||
-	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+			(vcpu->arch.hfscr & HFSCR_TM))
 		msr |= MSR_TM;
 	msr = msr_check_and_set(msr);
 
@@ -4608,8 +4621,9 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
 		msr |= MSR_VEC;
 	if (cpu_has_feature(CPU_FTR_VSX))
 		msr |= MSR_VSX;
-	if (cpu_has_feature(CPU_FTR_TM) ||
-	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+			(vcpu->arch.hfscr & HFSCR_TM))
 		msr |= MSR_TM;
 	msr = msr_check_and_set(msr);
 

arch/powerpc/kvm/book3s_hv_p9_entry.c

@@ -310,7 +310,7 @@ bool load_vcpu_state(struct kvm_vcpu *vcpu,
 		if (MSR_TM_ACTIVE(guest_msr)) {
 			kvmppc_restore_tm_hv(vcpu, guest_msr, true);
 			ret = true;
-		} else {
+		} else if (vcpu->arch.hfscr & HFSCR_TM) {
 			mtspr(SPRN_TEXASR, vcpu->arch.texasr);
 			mtspr(SPRN_TFHAR, vcpu->arch.tfhar);
 			mtspr(SPRN_TFIAR, vcpu->arch.tfiar);
@@ -346,10 +346,16 @@ void store_vcpu_state(struct kvm_vcpu *vcpu)
 		unsigned long guest_msr = vcpu->arch.shregs.msr;
 		if (MSR_TM_ACTIVE(guest_msr)) {
 			kvmppc_save_tm_hv(vcpu, guest_msr, true);
-		} else {
+		} else if (vcpu->arch.hfscr & HFSCR_TM) {
 			vcpu->arch.texasr = mfspr(SPRN_TEXASR);
 			vcpu->arch.tfhar = mfspr(SPRN_TFHAR);
 			vcpu->arch.tfiar = mfspr(SPRN_TFIAR);
+
+			if (!vcpu->arch.nested) {
+				vcpu->arch.load_tm++; /* see load_ebb comment */
+				if (!vcpu->arch.load_tm)
+					vcpu->arch.hfscr &= ~HFSCR_TM;
+			}
 		}
 	}
 #endif
@@ -641,8 +647,9 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 		msr |= MSR_VEC;
 	if (cpu_has_feature(CPU_FTR_VSX))
 		msr |= MSR_VSX;
-	if (cpu_has_feature(CPU_FTR_TM) ||
-	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+	if ((cpu_has_feature(CPU_FTR_TM) ||
+	    cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+			(vcpu->arch.hfscr & HFSCR_TM))
 		msr |= MSR_TM;
 	msr = msr_check_and_set(msr);
 	/* Save MSR for restore. This is after hard disable, so EE is clear. */