[PATCH] KVM/X86: vpmu migration, make perf_event associated with vcpu thread

[Wang Hui <john.whui1985@gmail.com>]

After applying Paolo's patch, vpmu's data was migrated correctly.
https://patchwork.kernel.org/patch/2850813/

But when I wrote a test module to make IA32_PMC1 to count the event of unhalted
cpu-cycles, after migration the value of IA32_PMC1 never grows up again. I found
that after migration perf_event was created exactly, but when it was created,
"current" is qemu's main thread which won't enter no-root mode, so the count of
perf_event will never increase.

I have tried pid in the struct of kvm_vcpu to get the vcpu thread's task_struct,
but after migration when create perf_event, pid is pointed to qemu's main thread
but not vcpu thread because of the pid switching in vcpu_load. I don't understand
this very well, I think vcpu is created in qemu_kvm_cpu_thread_fn, which is the
vcpu thread, use the pid of current is enough, why switch is needed?

Maybe I was totally wrong, so I kept these code unchanged, add a extra "tid" to
keep the vcpu thread's pid, and use this "tid" to get the task_struct of vcpu
thread when create perf_event.

Thanks
Wang Hui

Signed-off-by: Wang Hui <john.wanghui@huawei.com>
---
 arch/x86/kvm/pmu.c       | 8 +++++++-
 arch/x86/kvm/x86.c       | 6 ++++++
 include/linux/kvm_host.h | 1 +
 virt/kvm/kvm_main.c      | 1 +
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 5c4f631..676227e 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -173,6 +173,8 @@ static void reprogram_counter(struct kvm_pmc *pmc, u32 type,
 		.exclude_kernel = exclude_kernel,
 		.config = config,
 	};
+	struct task_struct *task = NULL;
+
 	if (in_tx)
 		attr.config |= HSW_IN_TX;
 	if (in_tx_cp)
@@ -180,7 +182,11 @@ static void reprogram_counter(struct kvm_pmc *pmc, u32 type,

 	attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc);

-	event = perf_event_create_kernel_counter(&attr, -1, current,
+	if (pmc->vcpu)
+		task = pid_task(pmc->vcpu->tid, PIDTYPE_PID);
+	if (!task)
+		task = current;
+	event = perf_event_create_kernel_counter(&attr, -1, task,
 						 intr ? kvm_perf_overflow_intr :
 						 kvm_perf_overflow, pmc);
 	if (IS_ERR(event)) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 21ef1ba..f1f0e8e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6704,11 +6704,17 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
 int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
 {
 	int r;
+	struct pid *cpu_thread_pid;

 	vcpu->arch.mtrr_state.have_fixed = 1;
 	r = vcpu_load(vcpu);
 	if (r)
 		return r;
+
+	cpu_thread_pid = get_task_pid(current, PIDTYPE_PID);
+	rcu_assign_pointer(vcpu->tid, cpu_thread_pid);
+	synchronize_rcu();
+
 	kvm_vcpu_reset(vcpu);
 	kvm_mmu_setup(vcpu);
 	vcpu_put(vcpu);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9523d2a..ad7af9d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -235,6 +235,7 @@ struct kvm_vcpu {
 	int guest_fpu_loaded, guest_xcr0_loaded;
 	wait_queue_head_t wq;
 	struct pid *pid;
+	struct pid *tid;
 	int sigset_active;
 	sigset_t sigset;
 	struct kvm_vcpu_stat stat;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a0aa84b..80bcce5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -242,6 +242,7 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_init);

 void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
 {
+	put_pid(vcpu->tid);
 	put_pid(vcpu->pid);
 	kvm_arch_vcpu_uninit(vcpu);
 	free_page((unsigned long)vcpu->run);