[xen master] x86/irq: forward pending interrupts to new destination in fixup_irqs()

[patchbot@xxxxxxx]

commit e2bb28d621584fce15c907002ddc7c6772644b64
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Jun 20 12:09:32 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jun 20 12:09:32 2024 +0200

    x86/irq: forward pending interrupts to new destination in fixup_irqs()
    
    fixup_irqs() is used to evacuate interrupts from to be offlined CPUs.  Given
    the CPU is to become offline, the normal migration logic used by Xen where 
the
    vector in the previous target(s) is left configured until the interrupt is
    received on the new destination is not suitable.
    
    Instead attempt to do as much as possible in order to prevent loosing
    interrupts.  If fixup_irqs() is called from the CPU to be offlined (as is
    currently the case for CPU hot unplug) attempt to forward pending vectors 
when
    interrupts that target the current CPU are migrated to a different 
destination.
    
    Additionally, for interrupts that have already been moved from the current 
CPU
    prior to the call to fixup_irqs() but that haven't been delivered to the new
    destination (iow: interrupts with move_in_progress set and the current CPU 
set
    in ->arch.old_cpu_mask) also check whether the previous vector is pending 
and
    forward it to the new destination.
    
    This allows us to remove the window with interrupts enabled at the bottom of
    fixup_irqs().  Such window wasn't safe anyway: references to the CPU to 
become
    offline are removed from interrupts masks, but the per-CPU vector_irq[] 
array
    is not updated to reflect those changes (as the CPU is going offline 
anyway).
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/arch/x86/include/asm/apic.h |  5 +++++
 xen/arch/x86/irq.c              | 46 +++++++++++++++++++++++++++++++++++------
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/include/asm/apic.h b/xen/arch/x86/include/asm/apic.h
index d1cb001fb4..7bd66dc6e1 100644
--- a/xen/arch/x86/include/asm/apic.h
+++ b/xen/arch/x86/include/asm/apic.h
@@ -132,6 +132,11 @@ static inline bool apic_isr_read(uint8_t vector)
             (vector & 0x1f)) & 1;
 }
 
+static inline bool apic_irr_read(unsigned int vector)
+{
+    return apic_read(APIC_IRR + (vector / 32 * 0x10)) & (1U << (vector % 32));
+}
+
 static inline u32 get_apic_id(void)
 {
     u32 id = apic_read(APIC_ID);
diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index d7f15c38af..9a611c79e0 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -2591,7 +2591,7 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
 
     for ( irq = 0; irq < nr_irqs; irq++ )
     {
-        bool break_affinity = false, set_affinity = true;
+        bool break_affinity = false, set_affinity = true, check_irr = false;
         unsigned int vector, cpu = smp_processor_id();
         cpumask_t *affinity = this_cpu(scratch_cpumask);
 
@@ -2644,6 +2644,25 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
              !cpu_online(cpu) &&
              cpumask_test_cpu(cpu, desc->arch.old_cpu_mask) )
         {
+            /*
+             * This to be offlined CPU was the target of an interrupt that's
+             * been moved, and the new destination target hasn't yet
+             * acknowledged any interrupt from it.
+             *
+             * We know the interrupt is configured to target the new CPU at
+             * this point, so we can check IRR for any pending vectors and
+             * forward them to the new destination.
+             *
+             * Note that for the other case of an interrupt movement being in
+             * progress (move_cleanup_count being non-zero) we know the new
+             * destination has already acked at least one interrupt from this
+             * source, and hence there's no need to forward any stale
+             * interrupts.
+             */
+            if ( apic_irr_read(desc->arch.old_vector) )
+                send_IPI_mask(cpumask_of(cpumask_any(desc->arch.cpu_mask)),
+                              desc->arch.vector);
+
             /*
              * This CPU is going offline, remove it from ->arch.old_cpu_mask
              * and possibly release the old vector if the old mask becomes
@@ -2684,6 +2703,14 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
         if ( desc->handler->disable )
             desc->handler->disable(desc);
 
+        /*
+         * If the current CPU is going offline and is (one of) the target(s) of
+         * the interrupt, signal to check whether there are any pending vectors
+         * to be handled in the local APIC after the interrupt has been moved.
+         */
+        if ( !cpu_online(cpu) && cpumask_test_cpu(cpu, desc->arch.cpu_mask) )
+            check_irr = true;
+
         if ( desc->handler->set_affinity )
             desc->handler->set_affinity(desc, affinity);
         else if ( !(warned++) )
@@ -2694,6 +2721,18 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
 
         cpumask_copy(affinity, desc->affinity);
 
+        if ( check_irr && apic_irr_read(vector) )
+            /*
+             * Forward pending interrupt to the new destination, this CPU is
+             * going offline and otherwise the interrupt would be lost.
+             *
+             * Do the IRR check as late as possible before releasing the irq
+             * desc in order for any in-flight interrupts to be delivered to
+             * the lapic.
+             */
+            send_IPI_mask(cpumask_of(cpumask_any(desc->arch.cpu_mask)),
+                          desc->arch.vector);
+
         spin_unlock(&desc->lock);
 
         if ( !verbose )
@@ -2705,11 +2744,6 @@ void fixup_irqs(const cpumask_t *mask, bool verbose)
             printk("Broke affinity for IRQ%u, new: {%*pbl}\n",
                    irq, CPUMASK_PR(affinity));
     }
-
-    /* That doesn't seem sufficient.  Give it 1ms. */
-    local_irq_enable();
-    mdelay(1);
-    local_irq_disable();
 }
 
 void fixup_eoi(void)
--
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