i8259: add -no-spurious-interrupt-hack option

This patch provides a way to optionally suppress spurious interrupts,
as a workaround for systems described below:

Some old operating systems do not handle spurious interrupts well,
and qemu tends to generate them significantly more often than
real hardware.

Examples:
  - Microport UNIX System V/386 v 2.1 (ca 1987)
    (The main problem I'm fixing: Without this patch, it panics
    sporadically when accessing the hard disk.)
  - AT&T UNIX System V/386 Release 4.0 Version 2.1a (ca 1991)
    See screenshot in "QEMU Official OS Support List":
    http://www.claunia.com/qemu/objectManager.php?sClass=application&iId=9
    (I don't have this system to test.)
  - A report about OS/2 boot lockup from 2004 by Hampa Hug:
    http://lists.nongnu.org/archive/html/qemu-devel/2004-09/msg00367.html
    (My patch was partially inspired by his.)
    Also: http://lists.nongnu.org/archive/html/qemu-devel/2005-06/msg00243.html
    (I don't have this system to test.)

Signed-off-by: Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>
Signed-off-by: malc <av1474@comtv.ru>

cpu-exec.c

@@ -329,11 +329,15 @@ int cpu_exec(CPUArchState *env)
                                                           0);
                             env->interrupt_request &= ~(CPU_INTERRUPT_HARD | CPU_INTERRUPT_VIRQ);
                             intno = cpu_get_pic_interrupt(env);
-                            qemu_log_mask(CPU_LOG_TB_IN_ASM, "Servicing hardware INT=0x%02x\n", intno);
-                            do_interrupt_x86_hardirq(env, intno, 1);
-                            /* ensure that no TB jump will be modified as
-                               the program flow was changed */
-                            next_tb = 0;
+                            if (intno >= 0) {
+                                qemu_log_mask(CPU_LOG_TB_IN_ASM,
+                                              "Servicing hardware INT=0x%02x\n",
+                                              intno);
+                                do_interrupt_x86_hardirq(env, intno, 1);
+                                /* ensure that no TB jump will be modified as
+                                   the program flow was changed */
+                                next_tb = 0;
+                            }
 #if !defined(CONFIG_USER_ONLY)
                         } else if ((interrupt_request & CPU_INTERRUPT_VIRQ) &&
                                    (env->eflags & IF_MASK) && 

hw/i8259.c

@@ -26,6 +26,7 @@
 #include "isa.h"
 #include "monitor.h"
 #include "qemu-timer.h"
+#include "sysemu.h"
 #include "i8259_internal.h"
 
 /* debug PIC */
@@ -193,6 +194,20 @@ int pic_read_irq(DeviceState *d)
                 pic_intack(slave_pic, irq2);
             } else {
                 /* spurious IRQ on slave controller */
+                if (no_spurious_interrupt_hack) {
+                    /* Pretend it was delivered and acknowledged.  If
+                     * it was spurious due to slave_pic->imr, then
+                     * as soon as the mask is cleared, the slave will
+                     * re-trigger IRQ2 on the master.  If it is spurious for
+                     * some other reason, make sure we don't keep trying
+                     * to half-process the same spurious interrupt over
+                     * and over again.
+                     */
+                    s->irr &= ~(1<<irq);
+                    s->last_irr &= ~(1<<irq);
+                    s->isr &= ~(1<<irq);
+                    return -1;
+                }
                 irq2 = 7;
             }
             intno = slave_pic->irq_base + irq2;
@@ -202,6 +217,9 @@ int pic_read_irq(DeviceState *d)
         pic_intack(s, irq);
     } else {
         /* spurious IRQ on host controller */
+        if (no_spurious_interrupt_hack) {
+            return -1;
+        }
         irq = 7;
         intno = s->irq_base + irq;
     }

qemu-options.hx

@@ -1189,6 +1189,18 @@ Windows 2000 is installed, you no longer need this option (this option
 slows down the IDE transfers).
 ETEXI
 
+DEF("no-spurious-interrupt-hack", 0, QEMU_OPTION_no_spurious_interrupt_hack,
+    "-no-spurious-interrupt-hack     disable delivery of spurious interrupts\n",
+    QEMU_ARCH_I386)
+STEXI
+@item -no-spurious-interrupt-hack
+@findex -no-spurious-interrupt-hack
+Use it as a workaround for operating systems that drive PICs in a way that
+can generate spurious interrupts, but the OS doesn't handle spurious
+interrupts gracefully.  (e.g. late 80s/early 90s versions of ATT UNIX
+and derivatives)
+ETEXI
+
 HXCOMM Deprecated by -rtc
 DEF("rtc-td-hack", 0, QEMU_OPTION_rtc_td_hack, "", QEMU_ARCH_I386)
 

sysemu.h

@@ -117,6 +117,7 @@ extern int graphic_depth;
 extern DisplayType display_type;
 extern const char *keyboard_layout;
 extern int win2k_install_hack;
+extern int no_spurious_interrupt_hack;
 extern int alt_grab;
 extern int ctrl_grab;
 extern int usb_enabled;

vl.c

@@ -204,6 +204,7 @@ CharDriverState *serial_hds[MAX_SERIAL_PORTS];
 CharDriverState *parallel_hds[MAX_PARALLEL_PORTS];
 CharDriverState *virtcon_hds[MAX_VIRTIO_CONSOLES];
 int win2k_install_hack = 0;
+int no_spurious_interrupt_hack = 0;
 int usb_enabled = 0;
 int singlestep = 0;
 int smp_cpus = 1;
@@ -3046,6 +3047,9 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_win2k_hack:
                 win2k_install_hack = 1;
                 break;
+            case QEMU_OPTION_no_spurious_interrupt_hack:
+                no_spurious_interrupt_hack = 1;
+                break;
             case QEMU_OPTION_rtc_td_hack: {
                 static GlobalProperty slew_lost_ticks[] = {
                     {