KVM: PPC: Book3S: Treat VTB as a per-subcore register, not per-thread

commit 88b02cf9 upstream.

POWER8 has one virtual timebase (VTB) register per subcore, not one
per CPU thread.  The HV KVM code currently treats VTB as a per-thread
register, which can lead to spurious soft lockup messages from guests
which use the VTB as the time source for the soft lockup detector.
(CPUs before POWER8 did not have the VTB register.)

For HV KVM, this fixes the problem by making only the primary thread
in each virtual core save and restore the VTB value.  With this,
the VTB state becomes part of the kvmppc_vcore structure.  This
also means that "piggybacking" of multiple virtual cores onto one
subcore is not possible on POWER8, because then the virtual cores
would share a single VTB register.

PR KVM emulates a VTB register, which is per-vcpu because PR KVM
has no notion of CPU threads or SMT.  For PR KVM we move the VTB
state into the kvmppc_vcpu_book3s struct.
Reported-by: Thomas Huth <thuth@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
[bwh: Backported to 3.16:
 - Adjust filenames, context
 - Drop changes to kvmppc_core_emulate_mfspr_pr(), can_piggyback_subcore(),
   kvmppc_copy_from_svcpu()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/powerpc/include/asm/kvm_book3s.h

@@ -83,6 +83,7 @@ struct kvmppc_vcpu_book3s {
 	u64 sdr1;
 	u64 hior;
 	u64 msr_mask;
+	u64 vtb;
 	u64 purr_offset;
 	u64 spurr_offset;
 #ifdef CONFIG_PPC_BOOK3S_32

arch/powerpc/include/asm/kvm_host.h

@@ -305,6 +305,7 @@ struct kvmppc_vcore {
 	u32 arch_compat;
 	ulong pcr;
 	ulong dpdes;		/* doorbell state (POWER8) */
+	ulong vtb;		/* virtual timebase */
 };
 
 #define VCORE_ENTRY_COUNT(vc)	((vc)->entry_exit_count & 0xff)
@@ -462,7 +463,6 @@ struct kvm_vcpu_arch {
 	ulong purr;
 	ulong spurr;
 	ulong ic;
-	ulong vtb;
 	ulong dscr;
 	ulong amr;
 	ulong uamor;

arch/powerpc/kernel/asm-offsets.c

@@ -506,7 +506,6 @@ int main(void)
 	DEFINE(VCPU_PURR, offsetof(struct kvm_vcpu, arch.purr));
 	DEFINE(VCPU_SPURR, offsetof(struct kvm_vcpu, arch.spurr));
 	DEFINE(VCPU_IC, offsetof(struct kvm_vcpu, arch.ic));
-	DEFINE(VCPU_VTB, offsetof(struct kvm_vcpu, arch.vtb));
 	DEFINE(VCPU_DSCR, offsetof(struct kvm_vcpu, arch.dscr));
 	DEFINE(VCPU_AMR, offsetof(struct kvm_vcpu, arch.amr));
 	DEFINE(VCPU_UAMOR, offsetof(struct kvm_vcpu, arch.uamor));
@@ -560,6 +559,7 @@ int main(void)
 	DEFINE(VCORE_LPCR, offsetof(struct kvmppc_vcore, lpcr));
 	DEFINE(VCORE_PCR, offsetof(struct kvmppc_vcore, pcr));
 	DEFINE(VCORE_DPDES, offsetof(struct kvmppc_vcore, dpdes));
+	DEFINE(VCORE_VTB, offsetof(struct kvmppc_vcore, vtb));
 	DEFINE(VCPU_SLB_E, offsetof(struct kvmppc_slb, orige));
 	DEFINE(VCPU_SLB_V, offsetof(struct kvmppc_slb, origv));
 	DEFINE(VCPU_SLB_SIZE, sizeof(struct kvmppc_slb));

arch/powerpc/kvm/book3s_hv.c

@@ -909,7 +909,7 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 		*val = get_reg_val(id, vcpu->arch.ic);
 		break;
 	case KVM_REG_PPC_VTB:
-		*val = get_reg_val(id, vcpu->arch.vtb);
+		*val = get_reg_val(id, vcpu->arch.vcore->vtb);
 		break;
 	case KVM_REG_PPC_CSIGR:
 		*val = get_reg_val(id, vcpu->arch.csigr);
@@ -1110,7 +1110,7 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 		vcpu->arch.ic = set_reg_val(id, *val);
 		break;
 	case KVM_REG_PPC_VTB:
-		vcpu->arch.vtb = set_reg_val(id, *val);
+		vcpu->arch.vcore->vtb = set_reg_val(id, *val);
 		break;
 	case KVM_REG_PPC_CSIGR:
 		vcpu->arch.csigr = set_reg_val(id, *val);

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -457,9 +457,11 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_207S)
 38:
 
 BEGIN_FTR_SECTION
-	/* DPDES is shared between threads */
+	/* DPDES and VTB are shared between threads */
 	ld	r8, VCORE_DPDES(r5)
+	ld	r7, VCORE_VTB(r5)
 	mtspr	SPRN_DPDES, r8
+	mtspr	SPRN_VTB, r7
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 
 	li	r0,1
@@ -736,10 +738,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
 	mtspr	SPRN_CIABR, r7
 	mtspr	SPRN_TAR, r8
 	ld	r5, VCPU_IC(r4)
-	ld	r6, VCPU_VTB(r4)
-	mtspr	SPRN_IC, r5
-	mtspr	SPRN_VTB, r6
 	ld	r8, VCPU_EBBHR(r4)
+	mtspr	SPRN_IC, r5
 	mtspr	SPRN_EBBHR, r8
 	ld	r5, VCPU_EBBRR(r4)
 	ld	r6, VCPU_BESCR(r4)
@@ -1147,10 +1147,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
 	stw	r6, VCPU_PSPB(r9)
 	std	r7, VCPU_FSCR(r9)
 	mfspr	r5, SPRN_IC
-	mfspr	r6, SPRN_VTB
 	mfspr	r7, SPRN_TAR
 	std	r5, VCPU_IC(r9)
-	std	r6, VCPU_VTB(r9)
 	std	r7, VCPU_TAR(r9)
 	mfspr	r8, SPRN_EBBHR
 	std	r8, VCPU_EBBHR(r9)
@@ -1442,9 +1440,11 @@ secondary_too_late:
 	isync
 
 BEGIN_FTR_SECTION
-	/* DPDES is shared between threads */
+	/* DPDES and VTB are shared between threads */
 	mfspr	r7, SPRN_DPDES
+	mfspr	r8, SPRN_VTB
 	std	r7, VCORE_DPDES(r5)
+	std	r8, VCORE_VTB(r5)
 	/* clear DPDES so we don't get guest doorbells in the host */
 	li	r8, 0
 	mtspr	SPRN_DPDES, r8

arch/powerpc/kvm/book3s_pr.c

@@ -1232,6 +1232,9 @@ static int kvmppc_get_one_reg_pr(struct kvm_vcpu *vcpu, u64 id,
 	case KVM_REG_PPC_HIOR:
 		*val = get_reg_val(id, to_book3s(vcpu)->hior);
 		break;
+	case KVM_REG_PPC_VTB:
+		*val = get_reg_val(id, to_book3s(vcpu)->vtb);
+		break;
 	case KVM_REG_PPC_LPCR:
 	case KVM_REG_PPC_LPCR_64:
 		/*
@@ -1268,6 +1271,9 @@ static int kvmppc_set_one_reg_pr(struct kvm_vcpu *vcpu, u64 id,
 		to_book3s(vcpu)->hior = set_reg_val(id, *val);
 		to_book3s(vcpu)->hior_explicit = true;
 		break;
+	case KVM_REG_PPC_VTB:
+		to_book3s(vcpu)->vtb = set_reg_val(id, *val);
+		break;
 	case KVM_REG_PPC_LPCR:
 	case KVM_REG_PPC_LPCR_64:
 		kvmppc_set_lpcr_pr(vcpu, set_reg_val(id, *val));