[PATCH 2/2] KVM: PPC: Book3S HV: Set RWMR on POWER8 so that PURR/SPURR count correctly

[Paul Mackerras <paulus@ozlabs.org>]

Although Linux doesn't use PURR and SPURR ((Scaled) Processor
Utilization of Resources Register), other OSes depend on them.
On POWER8 they count at a rate depending on whether the VCPU is
idle or running, the activity of the VCPU, and the value in the
RWMR (Region-Weighting Mode Register).  Hardware expects the
hypervisor to update the RWMR when a core is dispatched to reflect
the number of online VCPUs in the vcore.

This adds code to maintain a count in the vcore struct indicating
how many VCPUs are online.  In kvmppc_run_core we use that count
to set the RWMR register on POWER8.  If the core is split because
of a static or dynamic micro-threading mode, we use the value for
8 threads.  The RWMR value is not relevant when the host is
executing because Linux does not use the PURR or SPURR register,
so we don't bother saving and restoring the host value.

For the sake of old userspace which does not set the KVM_REG_PPC_ONLINE
register, we set online to 1 if it was 0 at the time of a KVM_RUN
ioctl.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
---
 arch/powerpc/include/asm/kvm_book3s.h |  1 +
 arch/powerpc/include/asm/reg.h        |  1 +
 arch/powerpc/kvm/book3s_hv.c          | 61 ++++++++++++++++++++++++++++++++++-
 3 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
index e7377b7..c1f3a87 100644
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h
@@ -104,6 +104,7 @@ struct kvmppc_vcore {
 	ulong vtb;		/* virtual timebase */
 	ulong conferring_threads;
 	unsigned int halt_poll_ns;
+	atomic_t online_count;
 };
 
 struct kvmppc_vcpu_book3s {
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index cb0f272..44b2be4 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -365,6 +365,7 @@
 #define SPRN_PSSCR	0x357	/* Processor Stop Status and Control Register (ISA 3.0) */
 #define SPRN_PSSCR_PR	0x337	/* PSSCR ISA 3.0, privileged mode access */
 #define SPRN_PMCR	0x374	/* Power Management Control Register */
+#define SPRN_RWMR	0x375	/* Region-Weighting Mode Register */
 
 /* HFSCR and FSCR bit numbers are the same */
 #define FSCR_SCV_LG	12	/* Enable System Call Vectored */
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 04bd717..f61dd9e 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -123,6 +123,32 @@ static bool no_mixing_hpt_and_radix;
 static void kvmppc_end_cede(struct kvm_vcpu *vcpu);
 static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu);
 
+/*
+ * RWMR values for POWER8.  These control the rate at which PURR
+ * and SPURR count and should be set according to the number of
+ * online threads in the vcore being run.
+ */
+#define RWMR_RPA_P8_1THREAD	0x164520C62609AECA
+#define RWMR_RPA_P8_2THREAD	0x7FFF2908450D8DA9
+#define RWMR_RPA_P8_3THREAD	0x164520C62609AECA
+#define RWMR_RPA_P8_4THREAD	0x199A421245058DA9
+#define RWMR_RPA_P8_5THREAD	0x164520C62609AECA
+#define RWMR_RPA_P8_6THREAD	0x164520C62609AECA
+#define RWMR_RPA_P8_7THREAD	0x164520C62609AECA
+#define RWMR_RPA_P8_8THREAD	0x164520C62609AECA
+
+static unsigned long p8_rwmr_values[MAX_SMT_THREADS + 1] = {
+	RWMR_RPA_P8_1THREAD,
+	RWMR_RPA_P8_1THREAD,
+	RWMR_RPA_P8_2THREAD,
+	RWMR_RPA_P8_3THREAD,
+	RWMR_RPA_P8_4THREAD,
+	RWMR_RPA_P8_5THREAD,
+	RWMR_RPA_P8_6THREAD,
+	RWMR_RPA_P8_7THREAD,
+	RWMR_RPA_P8_8THREAD,
+};
+
 static inline struct kvm_vcpu *next_runnable_thread(struct kvmppc_vcore *vc,
 		int *ip)
 {
@@ -1761,7 +1787,12 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 			vcpu->arch.vcore->tb_offset;
 		break;
 	case KVM_REG_PPC_ONLINE:
-		vcpu->arch.online = set_reg_val(id, *val);
+		i = set_reg_val(id, *val);
+		if (i && !vcpu->arch.online)
+			atomic_inc(&vcpu->arch.vcore->online_count);
+		else if (!i && vcpu->arch.online)
+			atomic_dec(&vcpu->arch.vcore->online_count);
+		vcpu->arch.online = i;
 		break;
 	default:
 		r = -EINVAL;
@@ -2856,6 +2887,25 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 		}
 	}
 
+	/*
+	 * On POWER8, set RWMR register.
+	 * Since it only affects PURR and SPURR, it doesn't affect
+	 * the host, so we don't save/restore the host value.
+	 */
+	if (is_power8) {
+		unsigned long rwmr_val = RWMR_RPA_P8_8THREAD;
+		int n_online = atomic_read(&vc->online_count);
+
+		/*
+		 * Use the 8-thread value if we're doing split-core
+		 * or if the vcore's online count looks bogus.
+		 */
+		if (split = 1 && threads_per_subcore = MAX_SMT_THREADS &&
+		    n_online >= 1 && n_online <= MAX_SMT_THREADS)
+			rwmr_val = p8_rwmr_values[n_online];
+		mtspr(SPRN_RWMR, rwmr_val);
+	}
+
 	/* Start all the threads */
 	active = 0;
 	for (sub = 0; sub < core_info.n_subcores; ++sub) {
@@ -3358,6 +3408,15 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	}
 #endif
 
+	/*
+	 * Force online to 1 for the sake of old userspace which doesn't
+	 * set it.
+	 */
+	if (!vcpu->arch.online) {
+		atomic_inc(&vcpu->arch.vcore->online_count);
+		vcpu->arch.online = 1;
+	}
+
 	kvmppc_core_prepare_to_enter(vcpu);
 
 	/* No need to go into the guest when all we'll do is come back out */
-- 
2.7.4