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Subject[PATCH 4.16 015/110] KVM: arm/arm64: Properly protect VGIC locks from IRQs
Date
4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andre Przywara <andre.przywara@arm.com>

commit 388d4359680b56dba82fe2ffca05871e9fd2b73e upstream.

As Jan reported [1], lockdep complains about the VGIC not being bullet
proof. This seems to be due to two issues:
- When commit 006df0f34930 ("KVM: arm/arm64: Support calling
vgic_update_irq_pending from irq context") promoted irq_lock and
ap_list_lock to _irqsave, we forgot two instances of irq_lock.
lockdeps seems to pick those up.
- If a lock is _irqsave, any other locks we take inside them should be
_irqsafe as well. So the lpi_list_lock needs to be promoted also.

This fixes both issues by simply making the remaining instances of those
locks _irqsave.
One irq_lock is addressed in a separate patch, to simplify backporting.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-May/575718.html

Cc: stable@vger.kernel.org
Fixes: 006df0f34930 ("KVM: arm/arm64: Support calling vgic_update_irq_pending from irq context")
Reported-by: Jan Glauber <jan.glauber@caviumnetworks.com>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
virt/kvm/arm/vgic/vgic-debug.c | 5 +++--
virt/kvm/arm/vgic/vgic-its.c | 10 ++++++----
virt/kvm/arm/vgic/vgic.c | 22 ++++++++++++++--------
3 files changed, 23 insertions(+), 14 deletions(-)

--- a/virt/kvm/arm/vgic/vgic-debug.c
+++ b/virt/kvm/arm/vgic/vgic-debug.c
@@ -211,6 +211,7 @@ static int vgic_debug_show(struct seq_fi
struct vgic_state_iter *iter = (struct vgic_state_iter *)v;
struct vgic_irq *irq;
struct kvm_vcpu *vcpu = NULL;
+ unsigned long flags;

if (iter->dist_id == 0) {
print_dist_state(s, &kvm->arch.vgic);
@@ -227,9 +228,9 @@ static int vgic_debug_show(struct seq_fi
irq = &kvm->arch.vgic.spis[iter->intid - VGIC_NR_PRIVATE_IRQS];
}

- spin_lock(&irq->irq_lock);
+ spin_lock_irqsave(&irq->irq_lock, flags);
print_irq_state(s, irq, vcpu);
- spin_unlock(&irq->irq_lock);
+ spin_unlock_irqrestore(&irq->irq_lock, flags);

return 0;
}
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -52,6 +52,7 @@ static struct vgic_irq *vgic_add_lpi(str
{
struct vgic_dist *dist = &kvm->arch.vgic;
struct vgic_irq *irq = vgic_get_irq(kvm, NULL, intid), *oldirq;
+ unsigned long flags;
int ret;

/* In this case there is no put, since we keep the reference. */
@@ -71,7 +72,7 @@ static struct vgic_irq *vgic_add_lpi(str
irq->intid = intid;
irq->target_vcpu = vcpu;

- spin_lock(&dist->lpi_list_lock);
+ spin_lock_irqsave(&dist->lpi_list_lock, flags);

/*
* There could be a race with another vgic_add_lpi(), so we need to
@@ -99,7 +100,7 @@ static struct vgic_irq *vgic_add_lpi(str
dist->lpi_list_count++;

out_unlock:
- spin_unlock(&dist->lpi_list_lock);
+ spin_unlock_irqrestore(&dist->lpi_list_lock, flags);

/*
* We "cache" the configuration table entries in our struct vgic_irq's.
@@ -315,6 +316,7 @@ static int vgic_copy_lpi_list(struct kvm
{
struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
struct vgic_irq *irq;
+ unsigned long flags;
u32 *intids;
int irq_count, i = 0;

@@ -330,7 +332,7 @@ static int vgic_copy_lpi_list(struct kvm
if (!intids)
return -ENOMEM;

- spin_lock(&dist->lpi_list_lock);
+ spin_lock_irqsave(&dist->lpi_list_lock, flags);
list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) {
if (i == irq_count)
break;
@@ -339,7 +341,7 @@ static int vgic_copy_lpi_list(struct kvm
continue;
intids[i++] = irq->intid;
}
- spin_unlock(&dist->lpi_list_lock);
+ spin_unlock_irqrestore(&dist->lpi_list_lock, flags);

*intid_ptr = intids;
return i;
--- a/virt/kvm/arm/vgic/vgic.c
+++ b/virt/kvm/arm/vgic/vgic.c
@@ -40,9 +40,13 @@ struct vgic_global kvm_vgic_global_state
* kvm->lock (mutex)
* its->cmd_lock (mutex)
* its->its_lock (mutex)
- * vgic_cpu->ap_list_lock
- * kvm->lpi_list_lock
- * vgic_irq->irq_lock
+ * vgic_cpu->ap_list_lock must be taken with IRQs disabled
+ * kvm->lpi_list_lock must be taken with IRQs disabled
+ * vgic_irq->irq_lock must be taken with IRQs disabled
+ *
+ * As the ap_list_lock might be taken from the timer interrupt handler,
+ * we have to disable IRQs before taking this lock and everything lower
+ * than it.
*
* If you need to take multiple locks, always take the upper lock first,
* then the lower ones, e.g. first take the its_lock, then the irq_lock.
@@ -69,8 +73,9 @@ static struct vgic_irq *vgic_get_lpi(str
{
struct vgic_dist *dist = &kvm->arch.vgic;
struct vgic_irq *irq = NULL;
+ unsigned long flags;

- spin_lock(&dist->lpi_list_lock);
+ spin_lock_irqsave(&dist->lpi_list_lock, flags);

list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) {
if (irq->intid != intid)
@@ -86,7 +91,7 @@ static struct vgic_irq *vgic_get_lpi(str
irq = NULL;

out_unlock:
- spin_unlock(&dist->lpi_list_lock);
+ spin_unlock_irqrestore(&dist->lpi_list_lock, flags);

return irq;
}
@@ -127,19 +132,20 @@ static void vgic_irq_release(struct kref
void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
{
struct vgic_dist *dist = &kvm->arch.vgic;
+ unsigned long flags;

if (irq->intid < VGIC_MIN_LPI)
return;

- spin_lock(&dist->lpi_list_lock);
+ spin_lock_irqsave(&dist->lpi_list_lock, flags);
if (!kref_put(&irq->refcount, vgic_irq_release)) {
- spin_unlock(&dist->lpi_list_lock);
+ spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
return;
};

list_del(&irq->lpi_list);
dist->lpi_list_count--;
- spin_unlock(&dist->lpi_list_lock);
+ spin_unlock_irqrestore(&dist->lpi_list_lock, flags);

kfree(irq);
}

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