KVM: PPC: Book3S HV: Enable guests to use large decrementer mode on POWER9

This allows userspace (e.g. QEMU) to enable large decrementer mode for
the guest when running on a POWER9 host, by setting the LPCR_LD bit in
the guest LPCR value.  With this, the guest exit code saves 64 bits of
the guest DEC value on exit.  Other places that use the guest DEC
value check the LPCR_LD bit in the guest LPCR value, and if it is set,
omit the 32-bit sign extension that would otherwise be done.

This doesn't change the DEC emulation used by PR KVM because PR KVM
is not supported on POWER9 yet.

This is partly based on an earlier patch by Oliver O'Halloran.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

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

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)

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

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;