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KVM: arm64: vgic-v3: Reinstate IRQ lock ordering for LPI xarray

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Zenghui reports that running a KVM guest with an assigned device and
lockdep enabled produces an unfriendly splat due to an inconsistent irq
context when taking the lpi_xa's spinlock.

This is no good as in rare cases the last reference to an LPI can get
dropped after injection of a cached LPI translation. In this case,
vgic_put_irq() will release the IRQ struct and take the lpi_xa's
spinlock to erase it from the xarray.

Reinstate the IRQ ordering and update the lockdep hint accordingly. Note
that there is no irqsave equivalent of might_lock(), so just explictly
grab and release the spinlock on lockdep kernels.

Reported-by: Zenghui Yu <yuzenghui@huawei.com>
Closes: https://lore.kernel.org/kvmarm/b4d7cb0f-f007-0b81-46d1-998b15cc14bc@huawei.com/
Fixes: 982f31bbb5 ("KVM: arm64: vgic-v3: Don't require IRQs be disabled for LPI xarray lock")
Signed-off-by: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/20251107184847.1784820-2-oupton@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Oliver Upton 2025-11-07 10:48:46 -08:00 committed by Marc Zyngier
parent 50e7cce81b
commit 75360a9a33
4 changed files with 32 additions and 16 deletions
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16
arch/arm64/kvm/vgic/vgic-debug.c
View File

@ -64,29 +64,37 @@ static void iter_next(struct kvm *kvm, struct vgic_state_iter *iter)
static int iter_mark_lpis(struct kvm *kvm)
{
struct vgic_dist *dist = &kvm->arch.vgic;
unsigned long intid, flags;
struct vgic_irq *irq;
unsigned long intid;
int nr_lpis = 0;
xa_lock_irqsave(&dist->lpi_xa, flags);
xa_for_each(&dist->lpi_xa, intid, irq) {
if (!vgic_try_get_irq_ref(irq))
continue;
xa_set_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);
__xa_set_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);
nr_lpis++;
}
xa_unlock_irqrestore(&dist->lpi_xa, flags);
return nr_lpis;
}
static void iter_unmark_lpis(struct kvm *kvm)
{
struct vgic_dist *dist = &kvm->arch.vgic;
unsigned long intid, flags;
struct vgic_irq *irq;
unsigned long intid;
xa_for_each_marked(&dist->lpi_xa, intid, irq, LPI_XA_MARK_DEBUG_ITER) {
xa_clear_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);
xa_lock_irqsave(&dist->lpi_xa, flags);
__xa_clear_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);
xa_unlock_irqrestore(&dist->lpi_xa, flags);
/* vgic_put_irq() expects to be called outside of the xa_lock */
vgic_put_irq(kvm, irq);
}
}

2
arch/arm64/kvm/vgic/vgic-init.c
View File

@ -53,7 +53,7 @@ void kvm_vgic_early_init(struct kvm *kvm)
{
struct vgic_dist *dist = &kvm->arch.vgic;
xa_init(&dist->lpi_xa);
xa_init_flags(&dist->lpi_xa, XA_FLAGS_LOCK_IRQ);
}
/* CREATION */

7
arch/arm64/kvm/vgic/vgic-its.c
View File

@ -78,6 +78,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
{
struct vgic_dist *dist = &kvm->arch.vgic;
struct vgic_irq *irq = vgic_get_irq(kvm, intid), *oldirq;
unsigned long flags;
int ret;
/* In this case there is no put, since we keep the reference. */
@ -88,7 +89,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
if (!irq)
return ERR_PTR(-ENOMEM);
ret = xa_reserve(&dist->lpi_xa, intid, GFP_KERNEL_ACCOUNT);
ret = xa_reserve_irq(&dist->lpi_xa, intid, GFP_KERNEL_ACCOUNT);
if (ret) {
kfree(irq);
return ERR_PTR(ret);
@ -103,7 +104,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
irq->target_vcpu = vcpu;
irq->group = 1;
xa_lock(&dist->lpi_xa);
xa_lock_irqsave(&dist->lpi_xa, flags);
/*
* There could be a race with another vgic_add_lpi(), so we need to
@ -125,7 +126,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
}
out_unlock:
xa_unlock(&dist->lpi_xa);
xa_unlock_irqrestore(&dist->lpi_xa, flags);
if (ret)
return ERR_PTR(ret);

23
arch/arm64/kvm/vgic/vgic.c
View File

@ -28,7 +28,7 @@ struct vgic_global kvm_vgic_global_state __ro_after_init = {
* kvm->arch.config_lock (mutex)
* its->cmd_lock (mutex)
* its->its_lock (mutex)
* vgic_dist->lpi_xa.xa_lock
* vgic_dist->lpi_xa.xa_lock must be taken with IRQs disabled
* vgic_cpu->ap_list_lock must be taken with IRQs disabled
* vgic_irq->irq_lock must be taken with IRQs disabled
*
@ -141,32 +141,39 @@ static __must_check bool vgic_put_irq_norelease(struct kvm *kvm, struct vgic_irq
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)
might_lock(&dist->lpi_xa.xa_lock);
/*
* Normally the lock is only taken when the refcount drops to 0.
* Acquire/release it early on lockdep kernels to make locking issues
* in rare release paths a bit more obvious.
*/
if (IS_ENABLED(CONFIG_LOCKDEP) && irq->intid >= VGIC_MIN_LPI) {
guard(spinlock_irqsave)(&dist->lpi_xa.xa_lock);
}
if (!__vgic_put_irq(kvm, irq))
return;
xa_lock(&dist->lpi_xa);
xa_lock_irqsave(&dist->lpi_xa, flags);
vgic_release_lpi_locked(dist, irq);
xa_unlock(&dist->lpi_xa);
xa_unlock_irqrestore(&dist->lpi_xa, flags);
}
static void vgic_release_deleted_lpis(struct kvm *kvm)
{
struct vgic_dist *dist = &kvm->arch.vgic;
unsigned long intid;
unsigned long flags, intid;
struct vgic_irq *irq;
xa_lock(&dist->lpi_xa);
xa_lock_irqsave(&dist->lpi_xa, flags);
xa_for_each(&dist->lpi_xa, intid, irq) {
if (irq->pending_release)
vgic_release_lpi_locked(dist, irq);
}
xa_unlock(&dist->lpi_xa);
xa_unlock_irqrestore(&dist->lpi_xa, flags);
}
void vgic_flush_pending_lpis(struct kvm_vcpu *vcpu)