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From: Gautam Menghani <gautam@linux.ibm.com>
To: mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu,
        aneesh.kumar@kernel.org, naveen.n.rao@linux.ibm.com
Cc: Gautam Menghani <gautam@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Vaibhav Jain <vaibhav@linux.ibm.com>
Subject: [PATCH v4] arch/powerpc/kvm: Add support for reading VPA counters for pseries guests
Date: Tue, 26 Mar 2024 15:10:34 +0530
Message-ID: <20240326094035.115835-1-gautam@linux.ibm.com>
Precedence: bulk
MIME-Version: 1.0
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PAPR hypervisor has introduced three new counters in the VPA area of
LPAR CPUs for KVM L2 guest (see [1] for terminology) observability - 2
for context switches from host to guest and vice versa, and 1 counter
for getting the total time spent inside the KVM guest. Add a tracepoint
that enables reading the counters for use by ftrace/perf. Note that this
tracepoint is only available for nestedv2 API (i.e, KVM on PowerVM).

Also maintain an aggregation of the context switch times in vcpu->arch.
This will be useful in getting the aggregate times with a pmu driver
which will be upstreamed in the near future.

[1] Terminology:
a. L1 refers to the VM (LPAR) booted on top of PAPR hypervisor
b. L2 refers to the KVM guest booted on top of L1.

Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Signed-off-by: Gautam Menghani <gautam@linux.ibm.com>
---
v1 -> v2:
1. Fix the build error due to invalid struct member reference.

v2 -> v3:
1. Move the counter disabling and zeroing code to a different function.
2. Move the get_lppaca() inside the tracepoint_enabled() branch.
3. Add the aggregation logic to maintain total context switch time.

v3 -> v4:
1. After vcpu_run, check the VPA flag instead of checking for tracepoint
being enabled for disabling the cs time accumulation.

 arch/powerpc/include/asm/kvm_host.h |  5 +++++
 arch/powerpc/include/asm/lppaca.h   | 11 ++++++++---
 arch/powerpc/kvm/book3s_hv.c        | 30 +++++++++++++++++++++++++++++
 arch/powerpc/kvm/trace_hv.h         | 25 ++++++++++++++++++++++++
 4 files changed, 68 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 8abac5321..d953b32dd 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -847,6 +847,11 @@ struct kvm_vcpu_arch {
 	gpa_t nested_io_gpr;
 	/* For nested APIv2 guests*/
 	struct kvmhv_nestedv2_io nestedv2_io;
+
+	/* Aggregate context switch and guest run time info (in ns) */
+	u64 l1_to_l2_cs_agg;
+	u64 l2_to_l1_cs_agg;
+	u64 l2_runtime_agg;
 #endif
 
 #ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
diff --git a/arch/powerpc/include/asm/lppaca.h b/arch/powerpc/include/asm/lppaca.h
index 61ec2447d..bda6b86b9 100644
--- a/arch/powerpc/include/asm/lppaca.h
+++ b/arch/powerpc/include/asm/lppaca.h
@@ -62,7 +62,8 @@ struct lppaca {
 	u8	donate_dedicated_cpu;	/* Donate dedicated CPU cycles */
 	u8	fpregs_in_use;
 	u8	pmcregs_in_use;
-	u8	reserved8[28];
+	u8	l2_accumul_cntrs_enable;  /* Enable usage of counters for KVM guest */
+	u8	reserved8[27];
 	__be64	wait_state_cycles;	/* Wait cycles for this proc */
 	u8	reserved9[28];
 	__be16	slb_count;		/* # of SLBs to maintain */
@@ -92,9 +93,13 @@ struct lppaca {
 	/* cacheline 4-5 */
 
 	__be32	page_ins;		/* CMO Hint - # page ins by OS */
-	u8	reserved12[148];
+	u8	reserved12[28];
+	volatile __be64 l1_to_l2_cs_tb;
+	volatile __be64 l2_to_l1_cs_tb;
+	volatile __be64 l2_runtime_tb;
+	u8 reserved13[96];
 	volatile __be64 dtl_idx;	/* Dispatch Trace Log head index */
-	u8	reserved13[96];
+	u8	reserved14[96];
 } ____cacheline_aligned;
 
 #define lppaca_of(cpu)	(*paca_ptrs[cpu]->lppaca_ptr)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 8e86eb577..dcd6edd3b 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4108,6 +4108,27 @@ static void vcpu_vpa_increment_dispatch(struct kvm_vcpu *vcpu)
 	}
 }
 
+static void do_trace_nested_cs_time(struct kvm_vcpu *vcpu)
+{
+	struct lppaca *lp = get_lppaca();
+	u64 l1_to_l2_ns, l2_to_l1_ns, l2_runtime_ns;
+
+	l1_to_l2_ns = tb_to_ns(be64_to_cpu(lp->l1_to_l2_cs_tb));
+	l2_to_l1_ns = tb_to_ns(be64_to_cpu(lp->l2_to_l1_cs_tb));
+	l2_runtime_ns = tb_to_ns(be64_to_cpu(lp->l2_runtime_tb));
+	trace_kvmppc_vcpu_exit_cs_time(vcpu, l1_to_l2_ns, l2_to_l1_ns,
+					l2_runtime_ns);
+	lp->l1_to_l2_cs_tb = 0;
+	lp->l2_to_l1_cs_tb = 0;
+	lp->l2_runtime_tb = 0;
+	lp->l2_accumul_cntrs_enable = 0;
+
+	// Maintain an aggregate of context switch times
+	vcpu->arch.l1_to_l2_cs_agg += l1_to_l2_ns;
+	vcpu->arch.l2_to_l1_cs_agg += l2_to_l1_ns;
+	vcpu->arch.l2_runtime_agg += l2_runtime_ns;
+}
+
 static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
 				     unsigned long lpcr, u64 *tb)
 {
@@ -4130,6 +4151,11 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
 	kvmppc_gse_put_u64(io->vcpu_run_input, KVMPPC_GSID_LPCR, lpcr);
 
 	accumulate_time(vcpu, &vcpu->arch.in_guest);
+
+	/* Enable the guest host context switch time tracking */
+	if (unlikely(trace_kvmppc_vcpu_exit_cs_time_enabled()))
+		get_lppaca()->l2_accumul_cntrs_enable = 1;
+
 	rc = plpar_guest_run_vcpu(0, vcpu->kvm->arch.lpid, vcpu->vcpu_id,
 				  &trap, &i);
 
@@ -4156,6 +4182,10 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
 
 	timer_rearm_host_dec(*tb);
 
+	/* Record context switch and guest_run_time data */
+	if (get_lppaca()->l2_accumul_cntrs_enable)
+		do_trace_nested_cs_time(vcpu);
+
 	return trap;
 }
 
diff --git a/arch/powerpc/kvm/trace_hv.h b/arch/powerpc/kvm/trace_hv.h
index 8d57c8428..ab19977c9 100644
--- a/arch/powerpc/kvm/trace_hv.h
+++ b/arch/powerpc/kvm/trace_hv.h
@@ -491,6 +491,31 @@ TRACE_EVENT(kvmppc_run_vcpu_enter,
 	TP_printk("VCPU %d: tgid=%d", __entry->vcpu_id, __entry->tgid)
 );
 
+TRACE_EVENT(kvmppc_vcpu_exit_cs_time,
+	TP_PROTO(struct kvm_vcpu *vcpu, u64 l1_to_l2_cs, u64 l2_to_l1_cs,
+		u64 l2_runtime),
+
+	TP_ARGS(vcpu, l1_to_l2_cs, l2_to_l1_cs, l2_runtime),
+
+	TP_STRUCT__entry(
+		__field(int,		vcpu_id)
+		__field(__u64,		l1_to_l2_cs_ns)
+		__field(__u64,		l2_to_l1_cs_ns)
+		__field(__u64,		l2_runtime_ns)
+	),
+
+	TP_fast_assign(
+		__entry->vcpu_id  = vcpu->vcpu_id;
+		__entry->l1_to_l2_cs_ns = l1_to_l2_cs;
+		__entry->l2_to_l1_cs_ns = l2_to_l1_cs;
+		__entry->l2_runtime_ns = l2_runtime;
+	),
+
+	TP_printk("VCPU %d: l1_to_l2_cs_time=%llu-ns l2_to_l1_cs_time=%llu-ns l2_runtime=%llu-ns",
+		__entry->vcpu_id,  __entry->l1_to_l2_cs_ns,
+		__entry->l2_to_l1_cs_ns, __entry->l2_runtime_ns)
+);
+
 TRACE_EVENT(kvmppc_run_vcpu_exit,
 	TP_PROTO(struct kvm_vcpu *vcpu),
 
-- 
2.43.2