[xen stable-4.17] x86/irq: deal with old_cpu_mask for interrupts in movement in fixup_irqs()

[patchbot@xxxxxxx]

commit a1c62c2ca689a90684fef36a108e7e71b951b7d5
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Wed Jun 26 14:11:33 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jun 26 14:11:33 2024 +0200

    x86/irq: deal with old_cpu_mask for interrupts in movement in fixup_irqs()
    
    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.
    
    Note that when the system is going down fixup_irqs() will be called by
    smp_send_stop() from CPU 0 with a mask with only CPU 0 on it, effectively
    asking to move all interrupts to the current caller (CPU 0) which is the 
only
    CPU to remain online.  In that case we don't care to migrate interrupts that
    are in the process of being moved, as it's likely we won't be able to move 
all
    interrupts to CPU 0 due to vector shortage anyway.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 817d1cd627be668c358d038f0fadbf7d24d417d3
    master date: 2024-06-18 15:14:49 +0200
---
 xen/arch/x86/irq.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index 2eac2de0b4..b1387cf6c9 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -2539,7 +2539,7 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
     for ( irq = 0; irq < nr_irqs; irq++ )
     {
         bool break_affinity = false, set_affinity = true;
-        unsigned int vector;
+        unsigned int vector, cpu = smp_processor_id();
         cpumask_t *affinity = this_cpu(scratch_cpumask);
 
         if ( irq == 2 )
@@ -2582,6 +2582,33 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
                                affinity);
         }
 
+        if ( desc->arch.move_in_progress &&
+             /*
+              * Only attempt to adjust the mask if the current CPU is going
+              * offline, otherwise the whole system is going down and leaving
+              * stale data in the masks is fine.
+              */
+             !cpu_online(cpu) &&
+             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
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.17