[xen stable-4.17] x86/irq: limit interrupt movement done by fixup_irqs()

[patchbot@xxxxxxx]

commit eeefc570559f129223ed8c0e24183cfdb1c39e5b
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Wed Jun 26 14:09:15 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jun 26 14:09:15 2024 +0200

    x86/irq: limit interrupt movement done by fixup_irqs()
    
    The current check used in fixup_irqs() to decide whether to move around
    interrupts is based on the affinity mask, but such mask can have all bits 
set,
    and hence is unlikely to be a subset of the input mask.  For example if an
    interrupt has an affinity mask of all 1s, any input to fixup_irqs() that's 
not
    an all set CPU mask would cause that interrupt to be shuffled around
    unconditionally.
    
    What fixup_irqs() care about is evacuating interrupts from CPUs not set on 
the
    input CPU mask, and for that purpose it should check whether the interrupt 
is
    assigned to a CPU not present in the input mask.  Assume that 
->arch.cpu_mask
    is a subset of the ->affinity mask, and keep the current logic that resets 
the
    ->affinity mask if the interrupt has to be shuffled around.
    
    Doing the affinity movement based on ->arch.cpu_mask requires removing the
    special handling to ->arch.cpu_mask done for high priority vectors, 
otherwise
    the adjustment done to cpu_mask makes them always skip the CPU interrupt
    movement.
    
    While there also adjust the comment as to the purpose of fixup_irqs().
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: c7564d7366d865cc407e3d64bca816d07edee174
    master date: 2024-06-12 14:30:40 +0200
---
 xen/arch/x86/include/asm/irq.h |  2 +-
 xen/arch/x86/irq.c             | 21 +++++++++++----------
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/xen/arch/x86/include/asm/irq.h b/xen/arch/x86/include/asm/irq.h
index 26850e5077..207c9fede2 100644
--- a/xen/arch/x86/include/asm/irq.h
+++ b/xen/arch/x86/include/asm/irq.h
@@ -136,7 +136,7 @@ void free_domain_pirqs(struct domain *d);
 int map_domain_emuirq_pirq(struct domain *d, int pirq, int irq);
 int unmap_domain_pirq_emuirq(struct domain *d, int pirq);
 
-/* Reset irq affinities to match the given CPU mask. */
+/* Evacuate interrupts assigned to CPUs not present in the input CPU mask. */
 void fixup_irqs(const cpumask_t *mask, bool verbose);
 void fixup_eoi(void);
 
diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index 5e6edc0905..2eac2de0b4 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -2529,7 +2529,7 @@ static int __init cf_check setup_dump_irqs(void)
 }
 __initcall(setup_dump_irqs);
 
-/* Reset irq affinities to match the given CPU mask. */
+/* Evacuate interrupts assigned to CPUs not present in the input CPU mask. */
 void fixup_irqs(const cpumask_t *mask, bool verbose)
 {
     unsigned int irq;
@@ -2553,19 +2553,15 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
 
         vector = irq_to_vector(irq);
         if ( vector >= FIRST_HIPRIORITY_VECTOR &&
-             vector <= LAST_HIPRIORITY_VECTOR )
+             vector <= LAST_HIPRIORITY_VECTOR &&
+             desc->handler == &no_irq_type )
         {
-            cpumask_and(desc->arch.cpu_mask, desc->arch.cpu_mask, mask);
-
             /*
              * This can in particular happen when parking secondary threads
              * during boot and when the serial console wants to use a PCI IRQ.
              */
-            if ( desc->handler == &no_irq_type )
-            {
-                spin_unlock(&desc->lock);
-                continue;
-            }
+            spin_unlock(&desc->lock);
+            continue;
         }
 
         if ( desc->arch.move_cleanup_count )
@@ -2586,7 +2582,12 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
                                affinity);
         }
 
-        if ( !desc->action || cpumask_subset(desc->affinity, mask) )
+        /*
+         * Avoid shuffling the interrupt around as long as current target CPUs
+         * are a subset of the input mask.  What fixup_irqs() cares about is
+         * evacuating interrupts from CPUs not in the input mask.
+         */
+        if ( !desc->action || cpumask_subset(desc->arch.cpu_mask, mask) )
         {
             spin_unlock(&desc->lock);
             continue;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.17