KVM: PPC: Book3S HV: Work around transactional memory bugs in POWER9

POWER9 has hardware bugs relating to transactional memory and thread
reconfiguration (changes to hardware SMT mode).  Specifically, the core
does not have enough storage to store a complete checkpoint of all the
architected state for all four threads.  The DD2.2 version of POWER9
includes hardware modifications designed to allow hypervisor software
to implement workarounds for these problems.  This patch implements
those workarounds in KVM code so that KVM guests see a full, working
transactional memory implementation.

The problems center around the use of TM suspended state, where the
CPU has a checkpointed state but execution is not transactional.  The
workaround is to implement a "fake suspend" state, which looks to the
guest like suspended state but the CPU does not store a checkpoint.
In this state, any instruction that would cause a transition to
transactional state (rfid, rfebb, mtmsrd, tresume) or would use the
checkpointed state (treclaim) causes a "soft patch" interrupt (vector
0x1500) to the hypervisor so that it can be emulated.  The trechkpt
instruction also causes a soft patch interrupt.

On POWER9 DD2.2, we avoid returning to the guest in any state which
would require a checkpoint to be present.  The trechkpt in the guest
entry path which would normally create that checkpoint is replaced by
either a transition to fake suspend state, if the guest is in suspend
state, or a rollback to the pre-transactional state if the guest is in
transactional state.  Fake suspend state is indicated by a flag in the
PACA plus a new bit in the PSSCR.  The new PSSCR bit is write-only and
reads back as 0.

On exit from the guest, if the guest is in fake suspend state, we still
do the treclaim instruction as we would in real suspend state, in order
to get into non-transactional state, but we do not save the resulting
register state since there was no checkpoint.

Emulation of the instructions that cause a softpatch interrupt is
handled in two paths.  If the guest is in real suspend mode, we call
kvmhv_p9_tm_emulation_early() to handle the cases where the guest is
transitioning to transactional state.  This is called before we do the
treclaim in the guest exit path; because we haven't done treclaim, we
can get back to the guest with the transaction still active.  If the
instruction is a case that kvmhv_p9_tm_emulation_early() doesn't
handle, or if the guest is in fake suspend state, then we proceed to
do the complete guest exit path and subsequently call
kvmhv_p9_tm_emulation() in host context with the MMU on.  This handles
all the cases including the cases that generate program interrupts
(illegal instruction or TM Bad Thing) and facility unavailable
interrupts.

The emulation is reasonably straightforward and is mostly concerned
with checking for exception conditions and updating the state of
registers such as MSR and CR0.  The treclaim emulation takes care to
ensure that the TEXASR register gets updated as if it were the guest
treclaim instruction that had done failure recording, not the treclaim
done in hypervisor state in the guest exit path.

With this, the KVM_CAP_PPC_HTM capability returns true (1) even if
transactional memory is not available to host userspace.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/kvm_asm.h

@@ -108,6 +108,8 @@
 
 /* book3s_hv */
 
+#define BOOK3S_INTERRUPT_HV_SOFTPATCH	0x1500
+
 /*
  * Special trap used to indicate to host that this is a
  * passthrough interrupt that could not be handled

arch/powerpc/include/asm/kvm_book3s.h

@@ -241,6 +241,10 @@ extern void kvmppc_update_lpcr(struct kvm *kvm, unsigned long lpcr,
 			unsigned long mask);
 extern void kvmppc_set_fscr(struct kvm_vcpu *vcpu, u64 fscr);
 
+extern int kvmhv_p9_tm_emulation_early(struct kvm_vcpu *vcpu);
+extern int kvmhv_p9_tm_emulation(struct kvm_vcpu *vcpu);
+extern void kvmhv_emulate_tm_rollback(struct kvm_vcpu *vcpu);
+
 extern void kvmppc_entry_trampoline(void);
 extern void kvmppc_hv_entry_trampoline(void);
 extern u32 kvmppc_alignment_dsisr(struct kvm_vcpu *vcpu, unsigned int inst);

arch/powerpc/include/asm/kvm_book3s_64.h

@@ -472,6 +472,49 @@ static inline void set_dirty_bits_atomic(unsigned long *map, unsigned long i,
 			set_bit_le(i, map);
 }
 
+static inline u64 sanitize_msr(u64 msr)
+{
+	msr &= ~MSR_HV;
+	msr |= MSR_ME;
+	return msr;
+}
+
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+static inline void copy_from_checkpoint(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.cr  = vcpu->arch.cr_tm;
+	vcpu->arch.xer = vcpu->arch.xer_tm;
+	vcpu->arch.lr  = vcpu->arch.lr_tm;
+	vcpu->arch.ctr = vcpu->arch.ctr_tm;
+	vcpu->arch.amr = vcpu->arch.amr_tm;
+	vcpu->arch.ppr = vcpu->arch.ppr_tm;
+	vcpu->arch.dscr = vcpu->arch.dscr_tm;
+	vcpu->arch.tar = vcpu->arch.tar_tm;
+	memcpy(vcpu->arch.gpr, vcpu->arch.gpr_tm,
+	       sizeof(vcpu->arch.gpr));
+	vcpu->arch.fp  = vcpu->arch.fp_tm;
+	vcpu->arch.vr  = vcpu->arch.vr_tm;
+	vcpu->arch.vrsave = vcpu->arch.vrsave_tm;
+}
+
+static inline void copy_to_checkpoint(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.cr_tm  = vcpu->arch.cr;
+	vcpu->arch.xer_tm = vcpu->arch.xer;
+	vcpu->arch.lr_tm  = vcpu->arch.lr;
+	vcpu->arch.ctr_tm = vcpu->arch.ctr;
+	vcpu->arch.amr_tm = vcpu->arch.amr;
+	vcpu->arch.ppr_tm = vcpu->arch.ppr;
+	vcpu->arch.dscr_tm = vcpu->arch.dscr;
+	vcpu->arch.tar_tm = vcpu->arch.tar;
+	memcpy(vcpu->arch.gpr_tm, vcpu->arch.gpr,
+	       sizeof(vcpu->arch.gpr));
+	vcpu->arch.fp_tm  = vcpu->arch.fp;
+	vcpu->arch.vr_tm  = vcpu->arch.vr;
+	vcpu->arch.vrsave_tm = vcpu->arch.vrsave;
+}
+#endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
+
 #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
 
 #endif /* __ASM_KVM_BOOK3S_64_H__ */

arch/powerpc/include/asm/kvm_book3s_asm.h

@@ -119,6 +119,7 @@ struct kvmppc_host_state {
 	u8 host_ipi;
 	u8 ptid;		/* thread number within subcore when split */
 	u8 tid;			/* thread number within whole core */
+	u8 fake_suspend;
 	struct kvm_vcpu *kvm_vcpu;
 	struct kvmppc_vcore *kvm_vcore;
 	void __iomem *xics_phys;

arch/powerpc/include/asm/kvm_host.h

@@ -610,6 +610,7 @@ struct kvm_vcpu_arch {
 	u64 tfhar;
 	u64 texasr;
 	u64 tfiar;
+	u64 orig_texasr;
 
 	u32 cr_tm;
 	u64 xer_tm;

arch/powerpc/include/asm/ppc-opcode.h

@@ -232,15 +232,18 @@
 #define PPC_INST_MSGSYNC		0x7c0006ec
 #define PPC_INST_MSGSNDP		0x7c00011c
 #define PPC_INST_MSGCLRP		0x7c00015c
+#define PPC_INST_MTMSRD			0x7c000164
 #define PPC_INST_MTTMR			0x7c0003dc
 #define PPC_INST_NOP			0x60000000
 #define PPC_INST_PASTE			0x7c20070d
 #define PPC_INST_POPCNTB		0x7c0000f4
 #define PPC_INST_POPCNTB_MASK		0xfc0007fe
 #define PPC_INST_POPCNTD		0x7c0003f4
 #define PPC_INST_POPCNTW		0x7c0002f4
+#define PPC_INST_RFEBB			0x4c000124
 #define PPC_INST_RFCI			0x4c000066
 #define PPC_INST_RFDI			0x4c00004e
+#define PPC_INST_RFID			0x4c000024
 #define PPC_INST_RFMCI			0x4c00004c
 #define PPC_INST_MFSPR			0x7c0002a6
 #define PPC_INST_MFSPR_DSCR		0x7c1102a6
@@ -277,6 +280,7 @@
 #define PPC_INST_TRECHKPT		0x7c0007dd
 #define PPC_INST_TRECLAIM		0x7c00075d
 #define PPC_INST_TABORT			0x7c00071d
+#define PPC_INST_TSR			0x7c0005dd
 
 #define PPC_INST_NAP			0x4c000364
 #define PPC_INST_SLEEP			0x4c0003a4

arch/powerpc/include/asm/reg.h

@@ -156,6 +156,8 @@
 #define PSSCR_SD		0x00400000 /* Status Disable */
 #define PSSCR_PLS	0xf000000000000000 /* Power-saving Level Status */
 #define PSSCR_GUEST_VIS	0xf0000000000003ff /* Guest-visible PSSCR fields */
+#define PSSCR_FAKE_SUSPEND	0x00000400 /* Fake-suspend bit (P9 DD2.2) */
+#define PSSCR_FAKE_SUSPEND_LG	10	   /* Fake-suspend bit position */
 
 /* Floating Point Status and Control Register (FPSCR) Fields */
 #define FPSCR_FX	0x80000000	/* FPU exception summary */
@@ -237,7 +239,12 @@
 #define SPRN_TFIAR	0x81	/* Transaction Failure Inst Addr   */
 #define SPRN_TEXASR	0x82	/* Transaction EXception & Summary */
 #define SPRN_TEXASRU	0x83	/* ''	   ''	   ''	 Upper 32  */
+#define   TEXASR_ABORT	__MASK(63-31) /* terminated by tabort or treclaim */
+#define   TEXASR_SUSP	__MASK(63-32) /* tx failed in suspended state */
+#define   TEXASR_HV	__MASK(63-34) /* MSR[HV] when failure occurred */
+#define   TEXASR_PR	__MASK(63-35) /* MSR[PR] when failure occurred */
 #define   TEXASR_FS	__MASK(63-36) /* TEXASR Failure Summary */
+#define   TEXASR_EXACT	__MASK(63-37) /* TFIAR value is exact */
 #define SPRN_TFHAR	0x80	/* Transaction Failure Handler Addr */
 #define SPRN_TIDR	144	/* Thread ID register */
 #define SPRN_CTRLF	0x088

arch/powerpc/kernel/asm-offsets.c

@@ -568,6 +568,7 @@ int main(void)
 	OFFSET(VCPU_TFHAR, kvm_vcpu, arch.tfhar);
 	OFFSET(VCPU_TFIAR, kvm_vcpu, arch.tfiar);
 	OFFSET(VCPU_TEXASR, kvm_vcpu, arch.texasr);
+	OFFSET(VCPU_ORIG_TEXASR, kvm_vcpu, arch.orig_texasr);
 	OFFSET(VCPU_GPR_TM, kvm_vcpu, arch.gpr_tm);
 	OFFSET(VCPU_FPRS_TM, kvm_vcpu, arch.fp_tm.fpr);
 	OFFSET(VCPU_VRS_TM, kvm_vcpu, arch.vr_tm.vr);
@@ -650,6 +651,7 @@ int main(void)
 	HSTATE_FIELD(HSTATE_HOST_IPI, host_ipi);
 	HSTATE_FIELD(HSTATE_PTID, ptid);
 	HSTATE_FIELD(HSTATE_TID, tid);
+	HSTATE_FIELD(HSTATE_FAKE_SUSPEND, fake_suspend);
 	HSTATE_FIELD(HSTATE_MMCR0, host_mmcr[0]);
 	HSTATE_FIELD(HSTATE_MMCR1, host_mmcr[1]);
 	HSTATE_FIELD(HSTATE_MMCRA, host_mmcr[2]);

arch/powerpc/kernel/cputable.c

@@ -569,7 +569,6 @@ static struct cpu_spec __initdata cpu_specs[] = {
 		.oprofile_type		= PPC_OPROFILE_INVALID,
 		.cpu_setup		= __setup_cpu_power9,
 		.cpu_restore		= __restore_cpu_power9,
-		.flush_tlb		= __flush_tlb_power9,
 		.machine_check_early	= __machine_check_early_realmode_p9,
 		.platform		= "power9",
 	},

arch/powerpc/kernel/exceptions-64s.S

@@ -1273,7 +1273,7 @@ EXC_REAL_BEGIN(denorm_exception_hv, 0x1500, 0x100)
 	bne+	denorm_assist
 #endif
 
-	KVMTEST_PR(0x1500)
+	KVMTEST_HV(0x1500)
 	EXCEPTION_PROLOG_PSERIES_1(denorm_common, EXC_HV)
 EXC_REAL_END(denorm_exception_hv, 0x1500, 0x100)
 
@@ -1285,7 +1285,7 @@ EXC_VIRT_END(denorm_exception, 0x5500, 0x100)
 EXC_VIRT_NONE(0x5500, 0x100)
 #endif
 
-TRAMP_KVM_SKIP(PACA_EXGEN, 0x1500)
+TRAMP_KVM_HV(PACA_EXGEN, 0x1500)
 
 #ifdef CONFIG_PPC_DENORMALISATION
 TRAMP_REAL_BEGIN(denorm_assist)

arch/powerpc/kvm/Makefile

@@ -74,16 +74,23 @@ kvm-hv-y += \
 	book3s_64_mmu_hv.o \
 	book3s_64_mmu_radix.o
 
+kvm-hv-$(CONFIG_PPC_TRANSACTIONAL_MEM) += \
+	book3s_hv_tm.o
+
 kvm-book3s_64-builtin-xics-objs-$(CONFIG_KVM_XICS) := \
 	book3s_hv_rm_xics.o book3s_hv_rm_xive.o
 
+kvm-book3s_64-builtin-tm-objs-$(CONFIG_PPC_TRANSACTIONAL_MEM) += \
+	book3s_hv_tm_builtin.o
+
 ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 kvm-book3s_64-builtin-objs-$(CONFIG_KVM_BOOK3S_64_HANDLER) += \
 	book3s_hv_hmi.o \
 	book3s_hv_rmhandlers.o \
 	book3s_hv_rm_mmu.o \
 	book3s_hv_ras.o \
 	book3s_hv_builtin.o \
+	$(kvm-book3s_64-builtin-tm-objs-y) \
 	$(kvm-book3s_64-builtin-xics-objs-y)
 endif
 

arch/powerpc/kvm/book3s_hv.c

@@ -1206,6 +1206,19 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			r = RESUME_GUEST;
 		}
 		break;
+
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+	case BOOK3S_INTERRUPT_HV_SOFTPATCH:
+		/*
+		 * This occurs for various TM-related instructions that
+		 * we need to emulate on POWER9 DD2.2.  We have already
+		 * handled the cases where the guest was in real-suspend
+		 * mode and was transitioning to transactional state.
+		 */
+		r = kvmhv_p9_tm_emulation(vcpu);
+		break;
+#endif
+
 	case BOOK3S_INTERRUPT_HV_RM_HARD:
 		r = RESUME_PASSTHROUGH;
 		break;
@@ -1978,7 +1991,9 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
 	 * turn off the HFSCR bit, which causes those instructions to trap.
 	 */
 	vcpu->arch.hfscr = mfspr(SPRN_HFSCR);
-	if (!cpu_has_feature(CPU_FTR_TM))
+	if (cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+		vcpu->arch.hfscr |= HFSCR_TM;
+	else if (!cpu_has_feature(CPU_FTR_TM_COMP))
 		vcpu->arch.hfscr &= ~HFSCR_TM;
 	if (cpu_has_feature(CPU_FTR_ARCH_300))
 		vcpu->arch.hfscr &= ~HFSCR_MSGP;
@@ -2242,6 +2257,7 @@ static void kvmppc_start_thread(struct kvm_vcpu *vcpu, struct kvmppc_vcore *vc)
 	tpaca = &paca[cpu];
 	tpaca->kvm_hstate.kvm_vcpu = vcpu;
 	tpaca->kvm_hstate.ptid = cpu - vc->pcpu;
+	tpaca->kvm_hstate.fake_suspend = 0;
 	/* Order stores to hstate.kvm_vcpu etc. before store to kvm_vcore */
 	smp_wmb();
 	tpaca->kvm_hstate.kvm_vcore = vc;