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KVM: arm64: vgic: Ensure the irq refcount is nonzero when taking a ref

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It will soon be possible for get() and put() calls to happen in
parallel, which means in most cases we must ensure the refcount is
nonzero when taking a new reference. Switch to using
vgic_try_get_irq_kref() where necessary, and document the few conditions
where an IRQ's refcount is guaranteed to be nonzero.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240221054253.3848076-10-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Oliver Upton 2024-02-21 05:42:52 +00:00
parent 864d4304ec
commit 50ac89bb70
2 changed files with 10 additions and 11 deletions
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18
arch/arm64/kvm/vgic/vgic-its.c
View File

@ -74,18 +74,11 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
* check that we don't add a second list entry with the same LPI.
*/
oldirq = xa_load(&dist->lpi_xa, intid);
if (oldirq) {
if (vgic_try_get_irq_kref(oldirq)) {
/* Someone was faster with adding this LPI, lets use that. */
kfree(irq);
irq = oldirq;
/*
* This increases the refcount, the caller is expected to
* call vgic_put_irq() on the returned pointer once it's
* finished with the IRQ.
*/
vgic_get_irq_kref(irq);
goto out_unlock;
}
@ -611,8 +604,8 @@ static struct vgic_irq *vgic_its_check_cache(struct kvm *kvm, phys_addr_t db,
raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
irq = __vgic_its_check_cache(dist, db, devid, eventid);
if (irq)
vgic_get_irq_kref(irq);
if (!vgic_try_get_irq_kref(irq))
irq = NULL;
raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
@ -658,6 +651,11 @@ static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
if (cte->irq)
__vgic_put_lpi_locked(kvm, cte->irq);
/*
* The irq refcount is guaranteed to be nonzero while holding the
* its_lock, as the ITE (and the reference it holds) cannot be freed.
*/
lockdep_assert_held(&its->its_lock);
vgic_get_irq_kref(irq);
cte->db = db;

3
arch/arm64/kvm/vgic/vgic.c
View File

@ -395,7 +395,8 @@ retry:
/*
* Grab a reference to the irq to reflect the fact that it is
* now in the ap_list.
* now in the ap_list. This is safe as the caller must already hold a
* reference on the irq.
*/
vgic_get_irq_kref(irq);
list_add_tail(&irq->ap_list, &vcpu->arch.vgic_cpu.ap_list_head);