The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d4a8061a7c5f7c27a2dc002ee4cb89b3e6637e44 Mon Sep 17 00:00:00 2001

From: Heyi Guo guoheyi@huawei.com Date: Tue, 27 Aug 2019 12:26:50 +0100 Subject: [PATCH] KVM: arm/arm64: vgic: Fix potential deadlock when ap_list is long

If the ap_list is longer than 256 entries, merge_final() in list_sort() will call the comparison callback with the same element twice, causing a deadlock in vgic_irq_cmp().

Fix it by returning early when irqa == irqb.

Cc: stable@vger.kernel.org # 4.7+ Fixes: 8e4447457965 ("KVM: arm/arm64: vgic-new: Add IRQ sorting") Signed-off-by: Zenghui Yu yuzenghui@huawei.com Signed-off-by: Heyi Guo guoheyi@huawei.com [maz: massaged commit log and patch, added Fixes and Cc-stable] Signed-off-by: Marc Zyngier maz@kernel.org Signed-off-by: Will Deacon will@kernel.org

diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c index 04786c8ec77e..ca5e6c6866a4 100644 --- a/virt/kvm/arm/vgic/vgic.c +++ b/virt/kvm/arm/vgic/vgic.c @@ -254,6 +254,13 @@ static int vgic_irq_cmp(void *priv, struct list_head *a, struct list_head *b) bool penda, pendb; int ret;

+ /* + * list_sort may call this function with the same element when + * the list is fairly long. + */ + if (unlikely(irqa == irqb)) + return 0; + raw_spin_lock(&irqa->irq_lock); raw_spin_lock_nested(&irqb->irq_lock, SINGLE_DEPTH_NESTING);