From: Paul Mackerras <paulus@xxxxxxxxx>
At the moment we call kvmppc_pin_guest_page() in kvmppc_update_vpa()
with two spinlocks held: the vcore lock and the vcpu->vpa_update_lock.
This is not good, since kvmppc_pin_guest_page() calls down_read() and
get_user_pages_fast(), both of which can sleep. This bug was introduced
in 2e25aa5f ("KVM: PPC: Book3S HV: Make virtual processor area
registration more robust").
This arranges to drop those spinlocks before calling
kvmppc_pin_guest_page() and re-take them afterwards. Dropping the
vcore lock in kvmppc_run_core() means we have to set the vcore_state
field to VCORE_RUNNING before we drop the lock, so that other vcpus
won't try to run this vcore.
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx>
Signed-off-by: Alexander Graf <agraf@xxxxxxx>
---
arch/powerpc/kvm/book3s_hv.c | 96 +++++++++++++++++++++++++++++-------------
1 files changed, 66 insertions(+), 30 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index d084e41..83e929e 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -268,24 +268,45 @@ static unsigned long do_h_register_vpa(struct kvm_vcpu *vcpu,
return err;
}
-static void kvmppc_update_vpa(struct kvm *kvm, struct kvmppc_vpa *vpap)
+static void kvmppc_update_vpa(struct kvm_vcpu *vcpu, struct kvmppc_vpa *vpap)
{
+ struct kvm *kvm = vcpu->kvm;
void *va;
unsigned long nb;
+ unsigned long gpa;
- vpap->update_pending = 0;
- va = NULL;
- if (vpap->next_gpa) {
- va = kvmppc_pin_guest_page(kvm, vpap->next_gpa, &nb);
- if (nb < vpap->len) {
- /*
- * If it's now too short, it must be that userspace
- * has changed the mappings underlying guest memory,
- * so unregister the region.
- */
+ /*
+ * We need to pin the page pointed to by vpap->next_gpa,
+ * but we can't call kvmppc_pin_guest_page under the lock
+ * as it does get_user_pages() and down_read(). So we
+ * have to drop the lock, pin the page, then get the lock
+ * again and check that a new area didn't get registered
+ * in the meantime.
+ */
+ for (;;) {
+ gpa = vpap->next_gpa;
+ spin_unlock(&vcpu->arch.vpa_update_lock);
+ va = NULL;
+ nb = 0;
+ if (gpa)
+ va = kvmppc_pin_guest_page(kvm, vpap->next_gpa, &nb);
+ spin_lock(&vcpu->arch.vpa_update_lock);
+ if (gpa == vpap->next_gpa)
+ break;
+ /* sigh... unpin that one and try again */
+ if (va)
kvmppc_unpin_guest_page(kvm, va);
- va = NULL;
- }
+ }
+
+ vpap->update_pending = 0;
+ if (va && nb < vpap->len) {
+ /*
+ * If it's now too short, it must be that userspace
+ * has changed the mappings underlying guest memory,
+ * so unregister the region.
+ */
+ kvmppc_unpin_guest_page(kvm, va);
+ va = NULL;
}
if (vpap->pinned_addr)
kvmppc_unpin_guest_page(kvm, vpap->pinned_addr);
@@ -296,20 +317,18 @@ static void kvmppc_update_vpa(struct kvm *kvm, struct kvmppc_vpa *vpap)
static void kvmppc_update_vpas(struct kvm_vcpu *vcpu)
{
- struct kvm *kvm = vcpu->kvm;
-
spin_lock(&vcpu->arch.vpa_update_lock);
if (vcpu->arch.vpa.update_pending) {
- kvmppc_update_vpa(kvm, &vcpu->arch.vpa);
+ kvmppc_update_vpa(vcpu, &vcpu->arch.vpa);
init_vpa(vcpu, vcpu->arch.vpa.pinned_addr);
}
if (vcpu->arch.dtl.update_pending) {
- kvmppc_update_vpa(kvm, &vcpu->arch.dtl);
+ kvmppc_update_vpa(vcpu, &vcpu->arch.dtl);
vcpu->arch.dtl_ptr = vcpu->arch.dtl.pinned_addr;
vcpu->arch.dtl_index = 0;
}
if (vcpu->arch.slb_shadow.update_pending)
- kvmppc_update_vpa(kvm, &vcpu->arch.slb_shadow);
+ kvmppc_update_vpa(vcpu, &vcpu->arch.slb_shadow);
spin_unlock(&vcpu->arch.vpa_update_lock);
}
@@ -800,12 +819,39 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
struct kvm_vcpu *vcpu, *vcpu0, *vnext;
long ret;
u64 now;
- int ptid, i;
+ int ptid, i, need_vpa_update;
/* don't start if any threads have a signal pending */
- list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
+ 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;
+ }
+
+ /*
+ * Initialize *vc, in particular vc->vcore_state, so we can
+ * drop the vcore lock if necessary.
+ */
+ vc->n_woken = 0;
+ vc->nap_count = 0;
+ vc->entry_exit_count = 0;
+ vc->vcore_state = VCORE_RUNNING;
+ vc->in_guest = 0;
+ vc->napping_threads = 0;
+
+ /*
+ * Updating any of the vpas requires calling kvmppc_pin_guest_page,
+ * which can't be called with any spinlocks held.
+ */
+ if (need_vpa_update) {
+ spin_unlock(&vc->lock);
+ list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
+ kvmppc_update_vpas(vcpu);
+ spin_lock(&vc->lock);
+ }
/*
* Make sure we are running on thread 0, and that
@@ -838,20 +884,10 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
if (vcpu->arch.ceded)
vcpu->arch.ptid = ptid++;
- vc->n_woken = 0;
- vc->nap_count = 0;
- vc->entry_exit_count = 0;
- vc->vcore_state = VCORE_RUNNING;
vc->stolen_tb += mftb() - vc->preempt_tb;
- vc->in_guest = 0;
vc->pcpu = smp_processor_id();
- vc->napping_threads = 0;
list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list) {
kvmppc_start_thread(vcpu);
- if (vcpu->arch.vpa.update_pending ||
- vcpu->arch.slb_shadow.update_pending ||
- vcpu->arch.dtl.update_pending)
- kvmppc_update_vpas(vcpu);
kvmppc_create_dtl_entry(vcpu, vc);
}
/* Grab any remaining hw threads so they can't go into the kernel */
--
1.6.0.2
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
