[PATCH 2/2] vmd: Synchronize with RCU freeing msi irq descs

[Keith Busch <keith.busch@intel.com>]

This patch fixes a potential race when disabling MSI/MSI-x on a VMD domain
device. If the vmd interrupt service is running, it may see a disabled
irq. We can synchronize rcu just before freeing the msi descriptor. This
is safe since the irq_desc lock isn't held, and the descriptor is valid
even though it is disabled. After vmd_msi_free, though, the handler is
reinitialiazed to handle_bad_irq, so we can't let the vmd isr's list
iteration see the disabled irq after this.

Signed-off-by: Keith Busch <keith.busch@intel.com>
---
 arch/x86/pci/vmd.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/pci/vmd.c b/arch/x86/pci/vmd.c
index 2294907..e3c9b9e 100644
--- a/arch/x86/pci/vmd.c
+++ b/arch/x86/pci/vmd.c
@@ -213,6 +213,8 @@ static void vmd_msi_free(struct irq_domain *domain,
 	struct vmd_irq *vmdirq = irq_get_chip_data(virq);
 	unsigned long flags;
 
+	synchronize_rcu();
+
 	/* XXX: Potential optimization to rebalance */
 	raw_spin_lock_irqsave(&list_lock, flags);
 	vmdirq->irq->count--;
-- 
2.7.2