[xen master] x86/irq: set accurate cpu_mask for high priority vectors used by external interrupts

[patchbot@xxxxxxx]

commit 68dda501d9889ae93008e43d9d558ad9e730fa42
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Fri Oct 24 09:22:08 2025 +0200
Commit:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
CommitDate: Wed Nov 26 09:46:17 2025 +0100

    x86/irq: set accurate cpu_mask for high priority vectors used by external 
interrupts
    
    Setting the irq descriptor target CPU mask of high priority interrupts to
    contain all online CPUs is not accurate.  External interrupts are
    exclusively delivered using physical destination mode, and hence can only
    target a single CPU.  Setting the descriptor CPU mask to contain all online
    CPUs makes it impossible for Xen to figure out which CPU the interrupt is
    really targeting.
    
    Instead handle high priority vectors used by external interrupts similarly
    to normal vectors, keeping the target CPU mask accurate.  Introduce
    specific code in _assign_irq_vector() to deal with moving high priority
    vectors across CPUs, this is needed at least for fixup_irqs() to be able to
    evacuate those if the target CPU goes offline.
    
    Fixes: fc0c3fa2ad5c ("x86/IO-APIC: fix setup of Xen internally used IRQs 
(take 2)")
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/irq.c     | 30 ++++++++++++++++++++++++------
 xen/arch/x86/smpboot.c |  3 ++-
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index fd34cd4cbe..92b8604dc8 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -547,6 +547,20 @@ static int _assign_irq_vector(struct irq_desc *desc, const 
cpumask_t *mask)
         cpumask_t tmp_mask;
 
         cpumask_and(&tmp_mask, mask, &cpu_online_map);
+
+        /*
+         * High priority vectors are reserved on all CPUs, hence moving them
+         * just requires changing the target CPU.  There's no need for vector
+         * allocation on the destination.
+         */
+        if ( old_vector >= FIRST_HIPRIORITY_VECTOR &&
+             old_vector <= LAST_HIPRIORITY_VECTOR )
+        {
+            cpumask_copy(desc->arch.cpu_mask,
+                         cpumask_of(cpumask_any(&tmp_mask)));
+            return 0;
+        }
+
         if (cpumask_intersects(&tmp_mask, desc->arch.cpu_mask)) {
             desc->arch.vector = old_vector;
             return 0;
@@ -756,12 +770,16 @@ void setup_vector_irq(unsigned int cpu)
         if ( !irq_desc_initialized(desc) )
             continue;
         vector = irq_to_vector(irq);
-        if ( vector >= FIRST_HIPRIORITY_VECTOR &&
-             vector <= LAST_HIPRIORITY_VECTOR )
-            cpumask_set_cpu(cpu, desc->arch.cpu_mask);
-        else if ( !cpumask_test_cpu(cpu, desc->arch.cpu_mask) )
-            continue;
-        per_cpu(vector_irq, cpu)[vector] = irq;
+        if ( cpumask_test_cpu(cpu, desc->arch.cpu_mask) ||
+             /*
+              * High-priority vectors are reserved on all CPUs.  Set
+              * the vector to IRQ assignment on all CPUs, even if the
+              * interrupt is not targeting this CPU.  That makes
+              * shuffling those interrupts around CPUs easier.
+              */
+             (vector >= FIRST_HIPRIORITY_VECTOR &&
+              vector <= LAST_HIPRIORITY_VECTOR) )
+            per_cpu(vector_irq, cpu)[vector] = irq;
     }
 }
 
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 7fab555233..69cc9bbc6e 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -1464,7 +1464,8 @@ void __init smp_intr_init(void)
 
         desc = irq_to_desc(irq);
         desc->arch.vector = vector;
-        cpumask_copy(desc->arch.cpu_mask, &cpu_online_map);
+        cpumask_copy(desc->arch.cpu_mask, cpumask_of(cpu));
+        cpumask_setall(desc->affinity);
     }
 
     /* Direct IPI vectors. */
--
generated by git-patchbot for /home/xen/git/xen.git#master