Patchwork [06/10] KVM: PPC: Book3s HV: Don't access runnable threads list without vcore lock

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Submitter Paul Mackerras
Date Sept. 21, 2012, 5:37 a.m.
Message ID <20120921053731.GG15685@drongo>
Download mbox | patch
Permalink /patch/185582/
State New
Headers show

Comments

Paul Mackerras - Sept. 21, 2012, 5:37 a.m.
There were a few places where we were traversing the list of runnable
threads in a virtual core, i.e. vc->runnable_threads, without holding
the vcore spinlock.  This extends the places where we hold the vcore
spinlock to cover everywhere that we traverse that list.

Since we possibly need to sleep inside kvmppc_book3s_hv_page_fault,
this moves the call of it from kvmppc_handle_exit out to
kvmppc_vcpu_run, where we don't hold the vcore lock.

In kvmppc_vcore_blocked, we don't actually need to check whether
all vcpus are ceded and don't have any pending exceptions, since the
caller has already done that.  The caller (kvmppc_run_vcpu) wasn't
actually checking for pending exceptions, so we add that.

The change of if to while in kvmppc_run_vcpu is to make sure that we
never call kvmppc_remove_runnable() when the vcore state is RUNNING or
EXITING.

Signed-off-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/kvm_asm.h |    1 +
 arch/powerpc/kvm/book3s_hv.c       |   64 +++++++++++++++++-------------------
 2 files changed, 31 insertions(+), 34 deletions(-)
Alexander Graf - Sept. 24, 2012, 12:48 p.m.
On 21.09.2012, at 07:37, Paul Mackerras wrote:

> There were a few places where we were traversing the list of runnable
> threads in a virtual core, i.e. vc->runnable_threads, without holding
> the vcore spinlock.  This extends the places where we hold the vcore
> spinlock to cover everywhere that we traverse that list.
> 
> Since we possibly need to sleep inside kvmppc_book3s_hv_page_fault,
> this moves the call of it from kvmppc_handle_exit out to
> kvmppc_vcpu_run, where we don't hold the vcore lock.
> 
> In kvmppc_vcore_blocked, we don't actually need to check whether
> all vcpus are ceded and don't have any pending exceptions, since the
> caller has already done that.  The caller (kvmppc_run_vcpu) wasn't
> actually checking for pending exceptions, so we add that.
> 
> The change of if to while in kvmppc_run_vcpu is to make sure that we
> never call kvmppc_remove_runnable() when the vcore state is RUNNING or
> EXITING.
> 
> Signed-off-by: Paul Mackerras <paulus@samba.org>
> ---
> arch/powerpc/include/asm/kvm_asm.h |    1 +
> arch/powerpc/kvm/book3s_hv.c       |   64 +++++++++++++++++-------------------
> 2 files changed, 31 insertions(+), 34 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/kvm_asm.h b/arch/powerpc/include/asm/kvm_asm.h
> index 76fdcfe..fb99a21 100644
> --- a/arch/powerpc/include/asm/kvm_asm.h
> +++ b/arch/powerpc/include/asm/kvm_asm.h
> @@ -123,6 +123,7 @@
> #define RESUME_GUEST_NV         RESUME_FLAG_NV
> #define RESUME_HOST             RESUME_FLAG_HOST
> #define RESUME_HOST_NV          (RESUME_FLAG_HOST|RESUME_FLAG_NV)
> +#define RESUME_PAGE_FAULT	(1<<2)

I would actually prefer if you could move this to core specific code. How about

#define RESUME_ARCH1	(1 << 2)

and then in book3s_hv.c:

#define RESUME_PAGE_FAULT	(RESUME_GUEST | RESUME_ARCH1)


Alex

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Patch

diff --git a/arch/powerpc/include/asm/kvm_asm.h b/arch/powerpc/include/asm/kvm_asm.h
index 76fdcfe..fb99a21 100644
--- a/arch/powerpc/include/asm/kvm_asm.h
+++ b/arch/powerpc/include/asm/kvm_asm.h
@@ -123,6 +123,7 @@ 
 #define RESUME_GUEST_NV         RESUME_FLAG_NV
 #define RESUME_HOST             RESUME_FLAG_HOST
 #define RESUME_HOST_NV          (RESUME_FLAG_HOST|RESUME_FLAG_NV)
+#define RESUME_PAGE_FAULT	(1<<2)
 
 #define KVM_GUEST_MODE_NONE	0
 #define KVM_GUEST_MODE_GUEST	1
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index cd3dc12..bd3c5c1 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -466,7 +466,6 @@  static int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			      struct task_struct *tsk)
 {
 	int r = RESUME_HOST;
-	int srcu_idx;
 
 	vcpu->stat.sum_exits++;
 
@@ -526,16 +525,12 @@  static int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	 * have been handled already.
 	 */
 	case BOOK3S_INTERRUPT_H_DATA_STORAGE:
-		srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
-		r = kvmppc_book3s_hv_page_fault(run, vcpu,
-				vcpu->arch.fault_dar, vcpu->arch.fault_dsisr);
-		srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
+		r = RESUME_PAGE_FAULT;
 		break;
 	case BOOK3S_INTERRUPT_H_INST_STORAGE:
-		srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
-		r = kvmppc_book3s_hv_page_fault(run, vcpu,
-				kvmppc_get_pc(vcpu), 0);
-		srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
+		vcpu->arch.fault_dar = kvmppc_get_pc(vcpu);
+		vcpu->arch.fault_dsisr = 0;
+		r = RESUME_PAGE_FAULT;
 		break;
 	/*
 	 * This occurs if the guest executes an illegal instruction.
@@ -880,22 +875,24 @@  static int on_primary_thread(void)
  * Run a set of guest threads on a physical core.
  * Called with vc->lock held.
  */
-static int kvmppc_run_core(struct kvmppc_vcore *vc)
+static void kvmppc_run_core(struct kvmppc_vcore *vc)
 {
 	struct kvm_vcpu *vcpu, *vcpu0, *vnext;
 	long ret;
 	u64 now;
 	int ptid, i, need_vpa_update;
 	int srcu_idx;
+	struct kvm_vcpu *vcpus_to_update[threads_per_core];
 
 	/* don't start if any threads have a signal pending */
 	need_vpa_update = 0;
 	list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list) {
 		if (signal_pending(vcpu->arch.run_task))
-			return 0;
-		need_vpa_update |= vcpu->arch.vpa.update_pending |
-			vcpu->arch.slb_shadow.update_pending |
-			vcpu->arch.dtl.update_pending;
+			return;
+		if (vcpu->arch.vpa.update_pending ||
+		    vcpu->arch.slb_shadow.update_pending ||
+		    vcpu->arch.dtl.update_pending)
+			vcpus_to_update[need_vpa_update++] = vcpu;
 	}
 
 	/*
@@ -915,8 +912,8 @@  static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	 */
 	if (need_vpa_update) {
 		spin_unlock(&vc->lock);
-		list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
-			kvmppc_update_vpas(vcpu);
+		for (i = 0; i < need_vpa_update; ++i)
+			kvmppc_update_vpas(vcpus_to_update[i]);
 		spin_lock(&vc->lock);
 	}
 
@@ -933,8 +930,10 @@  static int kvmppc_run_core(struct kvmppc_vcore *vc)
 			vcpu->arch.ptid = ptid++;
 		}
 	}
-	if (!vcpu0)
-		return 0;		/* nothing to run */
+	if (!vcpu0) {
+		vc->vcore_state = VCORE_INACTIVE;
+		return;		/* nothing to run; should never happen */
+	}
 	list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
 		if (vcpu->arch.ceded)
 			vcpu->arch.ptid = ptid++;
@@ -987,6 +986,7 @@  static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	preempt_enable();
 	kvm_resched(vcpu);
 
+	spin_lock(&vc->lock);
 	now = get_tb();
 	list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list) {
 		/* cancel pending dec exception if dec is positive */
@@ -1010,7 +1010,6 @@  static int kvmppc_run_core(struct kvmppc_vcore *vc)
 		}
 	}
 
-	spin_lock(&vc->lock);
  out:
 	vc->vcore_state = VCORE_INACTIVE;
 	vc->preempt_tb = mftb();
@@ -1021,8 +1020,6 @@  static int kvmppc_run_core(struct kvmppc_vcore *vc)
 			wake_up(&vcpu->arch.cpu_run);
 		}
 	}
-
-	return 1;
 }
 
 /*
@@ -1046,20 +1043,11 @@  static void kvmppc_wait_for_exec(struct kvm_vcpu *vcpu, int wait_state)
 static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
 {
 	DEFINE_WAIT(wait);
-	struct kvm_vcpu *v;
-	int all_idle = 1;
 
 	prepare_to_wait(&vc->wq, &wait, TASK_INTERRUPTIBLE);
 	vc->vcore_state = VCORE_SLEEPING;
 	spin_unlock(&vc->lock);
-	list_for_each_entry(v, &vc->runnable_threads, arch.run_list) {
-		if (!v->arch.ceded || v->arch.pending_exceptions) {
-			all_idle = 0;
-			break;
-		}
-	}
-	if (all_idle)
-		schedule();
+	schedule();
 	finish_wait(&vc->wq, &wait);
 	spin_lock(&vc->lock);
 	vc->vcore_state = VCORE_INACTIVE;
@@ -1115,7 +1103,8 @@  static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 		vc->runner = vcpu;
 		n_ceded = 0;
 		list_for_each_entry(v, &vc->runnable_threads, arch.run_list)
-			n_ceded += v->arch.ceded;
+			if (!v->arch.pending_exceptions)
+				n_ceded += v->arch.ceded;
 		if (n_ceded == vc->n_runnable)
 			kvmppc_vcore_blocked(vc);
 		else
@@ -1136,8 +1125,9 @@  static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 	}
 
 	if (signal_pending(current)) {
-		if (vc->vcore_state == VCORE_RUNNING ||
-		    vc->vcore_state == VCORE_EXITING) {
+		while (vcpu->arch.state == KVMPPC_VCPU_RUNNABLE &&
+		       (vc->vcore_state == VCORE_RUNNING ||
+			vc->vcore_state == VCORE_EXITING)) {
 			spin_unlock(&vc->lock);
 			kvmppc_wait_for_exec(vcpu, TASK_UNINTERRUPTIBLE);
 			spin_lock(&vc->lock);
@@ -1157,6 +1147,7 @@  static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 int kvmppc_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu)
 {
 	int r;
+	int srcu_idx;
 
 	if (!vcpu->arch.sane) {
 		run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
@@ -1195,6 +1186,11 @@  int kvmppc_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu)
 		    !(vcpu->arch.shregs.msr & MSR_PR)) {
 			r = kvmppc_pseries_do_hcall(vcpu);
 			kvmppc_core_prepare_to_enter(vcpu);
+		} else if (r == RESUME_PAGE_FAULT) {
+			srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+			r = kvmppc_book3s_hv_page_fault(run, vcpu,
+				vcpu->arch.fault_dar, vcpu->arch.fault_dsisr);
+			srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
 		}
 	} while (r == RESUME_GUEST);