[Xen-devel] x86: adjust handling of interrupts coming in via legacy vectors

["Jan Beulich" <JBeulich@xxxxxxxx>]

The debugging code added in c/s 24707:96987c324a4f was hit a (small)
number of times (one report being
http://lists.xen.org/archives/html/xen-devel/2012-05/msg00332.html),
apparently always with a vector within the legacy range. Obviously,
besides legacy vectors not normally expected to be in use on systems
with IO-APIC(s), they should never make it to the IRQ migration logic.

This wasn't being prevented so far: Since we don't have a one-to-one
mapping between vectors and IRQs - legacy IRQs may have two vectors
associated with them (one used in either 8259A, the other used in one
of the IO-APICs) -, vector-to-IRQ translations for legacy vectors (as
used in do_IRQ()) would yield a valid IRQ number despite the IRQ
really being handled via an IO-APIC.

This gets changed here - disable_8259A_irq() zaps the legacy vector-to-
IRQ mapping, and enable_8259A_irq(), should it ever be called for a
particular interrupts, restores it.

Additionally, the spurious interrupt logic in do_IRQ() gets adjusted
too: Interrupts coming in via legacy vectors obviously didn't get
reported through the IO-APIC/LAPIC pair (as we never program these
vectors into any RTE), and hence shouldn't get ack_APIC_irq() called on
them. Instead, a new function (pointer) bogus_8259A_irq() gets used to
have the 8259A driver take care of the bogus interrupt (as outside of
automatice EOI mode it may need an EOI to be issued for it to prevent
other interrupts that may legitimately go through the 8259As from
getting masked out).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/i8259.c
+++ b/xen/arch/x86/i8259.c
@@ -85,7 +85,15 @@ BUILD_16_IRQS(0xc) BUILD_16_IRQS(0xd) BU
 
 static DEFINE_SPINLOCK(i8259A_lock);
 
-static void mask_and_ack_8259A_irq(struct irq_desc *);
+static void _mask_and_ack_8259A_irq(unsigned int irq);
+
+void (*__read_mostly bogus_8259A_irq)(unsigned int irq) =
+    _mask_and_ack_8259A_irq;
+
+static void mask_and_ack_8259A_irq(struct irq_desc *desc)
+{
+    _mask_and_ack_8259A_irq(desc->irq);
+}
 
 static unsigned int startup_8259A_irq(struct irq_desc *desc)
 {
@@ -133,20 +141,26 @@ static unsigned int cached_irq_mask = 0x
  */
 unsigned int __read_mostly io_apic_irqs;
 
-void disable_8259A_irq(struct irq_desc *desc)
+static void _disable_8259A_irq(unsigned int irq)
 {
-    unsigned int mask = 1 << desc->irq;
+    unsigned int mask = 1 << irq;
     unsigned long flags;
 
     spin_lock_irqsave(&i8259A_lock, flags);
     cached_irq_mask |= mask;
-    if (desc->irq & 8)
+    if (irq & 8)
         outb(cached_A1,0xA1);
     else
         outb(cached_21,0x21);
+    per_cpu(vector_irq, 0)[LEGACY_VECTOR(irq)] = -1;
     spin_unlock_irqrestore(&i8259A_lock, flags);
 }
 
+void disable_8259A_irq(struct irq_desc *desc)
+{
+    _disable_8259A_irq(desc->irq);
+}
+
 void enable_8259A_irq(struct irq_desc *desc)
 {
     unsigned int mask = ~(1 << desc->irq);
@@ -154,6 +168,7 @@ void enable_8259A_irq(struct irq_desc *d
 
     spin_lock_irqsave(&i8259A_lock, flags);
     cached_irq_mask &= mask;
+    per_cpu(vector_irq, 0)[LEGACY_VECTOR(desc->irq)] = desc->irq;
     if (desc->irq & 8)
         outb(cached_A1,0xA1);
     else
@@ -226,9 +241,9 @@ static inline int i8259A_irq_real(unsign
  * first, _then_ send the EOI, and the order of EOI
  * to the two 8259s is important!
  */
-static void mask_and_ack_8259A_irq(struct irq_desc *desc)
+static void _mask_and_ack_8259A_irq(unsigned int irq)
 {
-    unsigned int irqmask = 1 << desc->irq;
+    unsigned int irqmask = 1 << irq;
     unsigned long flags;
 
     spin_lock_irqsave(&i8259A_lock, flags);
@@ -252,15 +267,15 @@ static void mask_and_ack_8259A_irq(struc
     cached_irq_mask |= irqmask;
 
  handle_real_irq:
-    if (desc->irq & 8) {
+    if (irq & 8) {
         inb(0xA1);              /* DUMMY - (do we need this?) */
         outb(cached_A1,0xA1);
-        outb(0x60 + (desc->irq & 7), 0xA0);/* 'Specific EOI' to slave */
+        outb(0x60 + (irq & 7), 0xA0);/* 'Specific EOI' to slave */
         outb(0x62,0x20);        /* 'Specific EOI' to master-IRQ2 */
     } else {
         inb(0x21);              /* DUMMY - (do we need this?) */
         outb(cached_21,0x21);
-        outb(0x60 + desc->irq, 0x20);/* 'Specific EOI' to master */
+        outb(0x60 + irq, 0x20);/* 'Specific EOI' to master */
     }
     spin_unlock_irqrestore(&i8259A_lock, flags);
     return;
@@ -269,7 +284,7 @@ static void mask_and_ack_8259A_irq(struc
     /*
      * this is the slow path - should happen rarely.
      */
-    if (i8259A_irq_real(desc->irq))
+    if (i8259A_irq_real(irq))
         /*
          * oops, the IRQ _is_ in service according to the
          * 8259A - not spurious, go handle it.
@@ -283,7 +298,7 @@ static void mask_and_ack_8259A_irq(struc
          * lets ACK and report it. [once per IRQ]
          */
         if (!(spurious_irq_mask & irqmask)) {
-            printk("spurious 8259A interrupt: IRQ%d.\n", desc->irq);
+            printk("spurious 8259A interrupt: IRQ%d.\n", irq);
             spurious_irq_mask |= irqmask;
         }
         /*
@@ -352,13 +367,19 @@ void __devinit init_8259A(int auto_eoi)
                                is to be investigated) */
 
     if (auto_eoi)
+    {
         /*
          * in AEOI mode we just have to mask the interrupt
          * when acking.
          */
         i8259A_irq_type.ack = disable_8259A_irq;
+        bogus_8259A_irq = _disable_8259A_irq;
+    }
     else
+    {
         i8259A_irq_type.ack = mask_and_ack_8259A_irq;
+        bogus_8259A_irq = _mask_and_ack_8259A_irq;
+    }
 
     udelay(100);            /* wait for 8259A to initialize */
 
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -811,9 +811,12 @@ void do_IRQ(struct cpu_user_regs *regs)
         if (direct_apic_vector[vector] != NULL) {
             (*direct_apic_vector[vector])(regs);
         } else {
-            ack_APIC_irq();
-            printk("%s: %d.%d No irq handler for vector (irq %d)\n",
-                   __func__, smp_processor_id(), vector, irq);
+            if ( vector < FIRST_LEGACY_VECTOR || vector > LAST_LEGACY_VECTOR )
+                ack_APIC_irq();
+            else
+                bogus_8259A_irq(vector - FIRST_LEGACY_VECTOR);
+            printk("CPU%u: No handler for vector %02x (IRQ %d)\n",
+                   smp_processor_id(), vector, irq);
             TRACE_1D(TRC_HW_IRQ_UNMAPPED_VECTOR, vector);
         }
         goto out_no_unlock;
--- a/xen/include/asm-x86/irq.h
+++ b/xen/include/asm-x86/irq.h
@@ -104,6 +104,7 @@ void mask_8259A(void);
 void unmask_8259A(void);
 void init_8259A(int aeoi);
 void make_8259A_irq(unsigned int irq);
+extern void (*bogus_8259A_irq)(unsigned int irq);
 int i8259A_suspend(void);
 int i8259A_resume(void);

Attachment: x86-spurious-8259A-irq.patch
Description: Text document

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