Commit 081f323b authored by Paul Mackerras's avatar Paul Mackerras Committed by Avi Kivity
Browse files

KVM: PPC: Book3S HV: Drop locks around call to kvmppc_pin_guest_page 



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: default avatarPaul Mackerras <paulus@samba.org>
Acked-by: default avatarAlexander Graf <agraf@suse.de>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent f961f728

arch/powerpc/kvm/book3s_hv.c

+66 −30
Original line number Diff line number Diff line
@@ -268,16 +268,38 @@ 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;

	/*

	 * 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;

	if (vpap->next_gpa) {

		nb = 0;

		if (gpa)

			va = kvmppc_pin_guest_page(kvm, vpap->next_gpa, &nb);

		if (nb < vpap->len) {

		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);

	}



	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,
@@ -286,7 +308,6 @@ static void kvmppc_update_vpa(struct kvm *kvm, struct kvmppc_vpa *vpap) 
		kvmppc_unpin_guest_page(kvm, va);

		va = NULL;

	}

	}

	if (vpap->pinned_addr)

		kvmppc_unpin_guest_page(kvm, vpap->pinned_addr);

	vpap->pinned_addr = va;
@@ -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 */

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