# Commit 87f37449d586b4d407b75235bb0a171e018e25ec
# Date 2023-11-02 10:50:59 +0100
# Author Roger Pau Monné <roger.pau@citrix.com>
# Committer Jan Beulich <jbeulich@suse.com>
x86/i8259: do not assume interrupts always target CPU0

Sporadically we have seen the following during AP bringup on AMD platforms
only:

microcode: CPU59 updated from revision 0x830107a to 0x830107a, date = 2023-05-17
microcode: CPU60 updated from revision 0x830104d to 0x830107a, date = 2023-05-17
CPU60: No irq handler for vector 27 (IRQ -2147483648)
microcode: CPU61 updated from revision 0x830107a to 0x830107a, date = 2023-05-17

This is similar to the issue raised on Linux commit 36e9e1eab777e, where they
observed i8259 (active) vectors getting delivered to CPUs different than 0.

On AMD or Hygon platforms adjust the target CPU mask of i8259 interrupt
descriptors to contain all possible CPUs, so that APs will reserve the vector
at startup if any legacy IRQ is still delivered through the i8259.  Note that
if the IO-APIC takes over those interrupt descriptors the CPU mask will be
reset.

Spurious i8259 interrupt vectors however (IRQ7 and IRQ15) can be injected even
when all i8259 pins are masked, and hence would need to be handled on all CPUs.

Continue to reserve PIC vectors on CPU0 only, but do check for such spurious
interrupts on all CPUs if the vendor is AMD or Hygon.  Note that once the
vectors get used by devices detecting PIC spurious interrupts will no longer be
possible, however the device driver should be able to cope with spurious
interrupts.  Such PIC spurious interrupts occurring when the vector is in use
by a local APIC routed source will lead to an extra EOI, which might
unintentionally clear a different vector from ISR.  Note this is already the
current behavior, so assume it's infrequent enough to not cause real issues.

Finally, adjust the printed message to display the CPU where the spurious
interrupt has been received, so it looks like:

microcode: CPU1 updated from revision 0x830107a to 0x830107a, date = 2023-05-17
cpu1: spurious 8259A interrupt: IRQ7
microcode: CPU2 updated from revision 0x830104d to 0x830107a, date = 2023-05-17

Amends: 3fba06ba9f8b ('x86/IRQ: re-use legacy vector ranges on APs')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/i8259.c
+++ b/xen/arch/x86/i8259.c
@@ -222,7 +222,8 @@ static bool _mask_and_ack_8259A_irq(unsi
         is_real_irq = false;
         /* Report spurious IRQ, once per IRQ line. */
         if (!(spurious_irq_mask & irqmask)) {
-            printk("spurious 8259A interrupt: IRQ%d.\n", irq);
+            printk("cpu%u: spurious 8259A interrupt: IRQ%u\n",
+                   smp_processor_id(), irq);
             spurious_irq_mask |= irqmask;
         }
         /*
@@ -349,7 +350,23 @@ void __init init_IRQ(void)
             continue;
         desc->handler = &i8259A_irq_type;
         per_cpu(vector_irq, cpu)[LEGACY_VECTOR(irq)] = irq;
-        cpumask_copy(desc->arch.cpu_mask, cpumask_of(cpu));
+
+        /*
+         * The interrupt affinity logic never targets interrupts to offline
+         * CPUs, hence it's safe to use cpumask_all here.
+         *
+         * Legacy PIC interrupts are only targeted to CPU0, but depending on
+         * the platform they can be distributed to any online CPU in hardware.
+         * Note this behavior has only been observed on AMD hardware. In order
+         * to cope install all active legacy vectors on all CPUs.
+         *
+         * IO-APIC will change the destination mask if/when taking ownership of
+         * the interrupt.
+         */
+        cpumask_copy(desc->arch.cpu_mask,
+                     (boot_cpu_data.x86_vendor &
+                      (X86_VENDOR_AMD | X86_VENDOR_HYGON) ? &cpumask_all
+                                                          : cpumask_of(cpu)));
         desc->arch.vector = LEGACY_VECTOR(irq);
     }
     
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -1920,7 +1920,16 @@ void do_IRQ(struct cpu_user_regs *regs)
                 kind = "";
             if ( !(vector >= FIRST_LEGACY_VECTOR &&
                    vector <= LAST_LEGACY_VECTOR &&
-                   !smp_processor_id() &&
+                   (!smp_processor_id() ||
+                    /*
+                     * For AMD/Hygon do spurious PIC interrupt
+                     * detection on all CPUs, as it has been observed
+                     * that during unknown circumstances spurious PIC
+                     * interrupts have been delivered to CPUs
+                     * different than the BSP.
+                     */
+                    (boot_cpu_data.x86_vendor & (X86_VENDOR_AMD |
+                                                 X86_VENDOR_HYGON))) &&
                    bogus_8259A_irq(vector - FIRST_LEGACY_VECTOR)) )
             {
                 printk("CPU%u: No irq handler for vector %02x (IRQ %d%s)\n",