[PATCH for-4.19 7/9] x86/irq: deal with old_cpu_mask for interrupts in movement in fixup_irqs()

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Given the current logic it's possible for ->arch.old_cpu_mask to get out of
sync: if a CPU set in old_cpu_mask is offlined and then onlined
again without old_cpu_mask having been updated the data in the mask will no
longer be accurate, as when brought back online the CPU will no longer have
old_vector configured to handle the old interrupt source.

If there's an interrupt movement in progress, and the to be offlined CPU (which
is the call context) is in the old_cpu_mask clear it and update the mask, so it
doesn't contain stale data.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/irq.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index ae8fa574d4e7..8822f382bfe4 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -2602,6 +2602,28 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
                             &cpu_online_map);
         }
 
+        if ( desc->arch.move_in_progress &&
+             !cpumask_test_cpu(cpu, &cpu_online_map) &&
+             cpumask_test_cpu(cpu, desc->arch.old_cpu_mask) )
+        {
+            /*
+             * This CPU is going offline, remove it from ->arch.old_cpu_mask
+             * and possibly release the old vector if the old mask becomes
+             * empty.
+             *
+             * Note cleaning ->arch.old_cpu_mask is required if the CPU is
+             * brought offline and then online again, as when re-onlined the
+             * per-cpu vector table will no longer have ->arch.old_vector
+             * setup, and hence ->arch.old_cpu_mask would be stale.
+             */
+            cpumask_clear_cpu(cpu, desc->arch.old_cpu_mask);
+            if ( cpumask_empty(desc->arch.old_cpu_mask) )
+            {
+                desc->arch.move_in_progress = 0;
+                release_old_vec(desc);
+            }
+        }
+
         /*
          * Avoid shuffling the interrupt around as long as current target CPUs
          * are a subset of the input mask.  What fixup_irqs() cares about is
-- 
2.44.0