diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 9c51ac4b8f36..3f879c802feb 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -579,7 +579,7 @@ struct kvm_vcpu_arch {
 	ulong mcsrr0;
 	ulong mcsrr1;
 	ulong mcsr;
-	u32 dec;
+	ulong dec;
 #ifdef CONFIG_BOOKE
 	u32 decar;
 #endif
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 8d1a365b8edc..ffbb1b359748 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1143,6 +1143,12 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
 	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC;
 	if (cpu_has_feature(CPU_FTR_ARCH_207S))
 		mask |= LPCR_AIL;
+	/*
+	 * On POWER9, allow userspace to enable large decrementer for the
+	 * guest, whether or not the host has it enabled.
+	 */
+	if (cpu_has_feature(CPU_FTR_ARCH_300))
+		mask |= LPCR_LD;
 
 	/* Broken 32-bit version of LPCR must not clear top bits */
 	if (preserve_top32)
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 4888dd494604..cc2a86bf0988 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -936,7 +936,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
 	mftb	r7
 	subf	r3,r7,r8
 	mtspr	SPRN_DEC,r3
-	stw	r3,VCPU_DEC(r4)
+	std	r3,VCPU_DEC(r4)
 
 	ld	r5, VCPU_SPRG0(r4)
 	ld	r6, VCPU_SPRG1(r4)
@@ -1048,7 +1048,13 @@ kvmppc_cede_reentry:		/* r4 = vcpu, r13 = paca */
 	li	r0, BOOK3S_INTERRUPT_EXTERNAL
 	bne	cr1, 12f
 	mfspr	r0, SPRN_DEC
-	cmpwi	r0, 0
+BEGIN_FTR_SECTION
+	/* On POWER9 check whether the guest has large decrementer enabled */
+	andis.	r8, r8, LPCR_LD@h
+	bne	15f
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
+	extsw	r0, r0
+15:	cmpdi	r0, 0
 	li	r0, BOOK3S_INTERRUPT_DECREMENTER
 	bge	5f
 
@@ -1475,12 +1481,18 @@ mc_cont:
 	mtspr	SPRN_SPURR,r4
 
 	/* Save DEC */
+	ld	r3, HSTATE_KVM_VCORE(r13)
 	mfspr	r5,SPRN_DEC
 	mftb	r6
+	/* On P9, if the guest has large decr enabled, don't sign extend */
+BEGIN_FTR_SECTION
+	ld	r4, VCORE_LPCR(r3)
+	andis.	r4, r4, LPCR_LD@h
+	bne	16f
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
 	extsw	r5,r5
-	add	r5,r5,r6
+16:	add	r5,r5,r6
 	/* r5 is a guest timebase value here, convert to host TB */
-	ld	r3,HSTATE_KVM_VCORE(r13)
 	ld	r4,VCORE_TB_OFFSET(r3)
 	subf	r5,r4,r5
 	std	r5,VCPU_DEC_EXPIRES(r9)
@@ -2402,8 +2414,15 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
 	mfspr	r3, SPRN_DEC
 	mfspr	r4, SPRN_HDEC
 	mftb	r5
+BEGIN_FTR_SECTION
+	/* On P9 check whether the guest has large decrementer mode enabled */
+	ld	r6, HSTATE_KVM_VCORE(r13)
+	ld	r6, VCORE_LPCR(r6)
+	andis.	r6, r6, LPCR_LD@h
+	bne	68f
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
 	extsw	r3, r3
-	EXTEND_HDEC(r4)
+68:	EXTEND_HDEC(r4)
 	cmpd	r3, r4
 	ble	67f
 	mtspr	SPRN_DEC, r4
diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
index c873ffe55362..4d8b4d6cebff 100644
--- a/arch/powerpc/kvm/emulate.c
+++ b/arch/powerpc/kvm/emulate.c
@@ -39,7 +39,7 @@ void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
 	unsigned long dec_nsec;
 	unsigned long long dec_time;
 
-	pr_debug("mtDEC: %x\n", vcpu->arch.dec);
+	pr_debug("mtDEC: %lx\n", vcpu->arch.dec);
 	hrtimer_try_to_cancel(&vcpu->arch.dec_timer);
 
 #ifdef CONFIG_PPC_BOOK3S
@@ -109,7 +109,7 @@ static int kvmppc_emulate_mtspr(struct kvm_vcpu *vcpu, int sprn, int rs)
 	case SPRN_TBWU: break;
 
 	case SPRN_DEC:
-		vcpu->arch.dec = spr_val;
+		vcpu->arch.dec = (u32) spr_val;
 		kvmppc_emulate_dec(vcpu);
 		break;