[Qemu-devel] [PATCH] APIC: add NMI and SMI IPI support

[Jan Kiszka]

While testing KGDB (yeah, it actually seem to make it into mainline!)
under QEMU, I failed to get it running in SMP mode. Reason: NMI IPIs are
not correctly handled by QEMU's emulated APIC.

To overcome this, the patch below introduces a new interruption request,
CPU_INTERRUPT_NMI, so that a VCPU can cleanly send this special
interrupt to other VCPUs. It also introduces HF_NMI_MASK which shall
ensure that NMIs are not recursively triggered, but I must confess that
this particular property was not really tested yet.

CPU_INTERRUPT_NMI is then trivially exploited by apic_bus_deliver to
send out both NMIs and (for the sake of completeness - it's untested as
well SMIs).

With this patch applied, I'm finally able to run (and potentially debug)
KGDB for Linux SMP guests.

Jan

---
 cpu-all.h            |    1 +
 cpu-exec.c           |    6 ++++++
 hw/apic.c            |    8 +++++++-
 target-i386/cpu.h    |    2 ++
 target-i386/helper.c |    2 ++
 5 files changed, 18 insertions(+), 1 deletion(-)

Index: b/hw/apic.c
===================================================================
--- a/hw/apic.c
+++ b/hw/apic.c
@@ -216,8 +216,14 @@ static void apic_bus_deliver(const uint3
             break;
 
         case APIC_DM_SMI:
+            foreach_apic(apic_iter, deliver_bitmask,
+                cpu_interrupt(apic_iter->cpu_env, CPU_INTERRUPT_SMI) );
+            return;
+
         case APIC_DM_NMI:
-            break;
+            foreach_apic(apic_iter, deliver_bitmask,
+                cpu_interrupt(apic_iter->cpu_env, CPU_INTERRUPT_NMI) );
+            return;
 
         case APIC_DM_INIT:
             /* normal INIT IPI sent to processors */
Index: b/cpu-all.h
===================================================================
--- a/cpu-all.h
+++ b/cpu-all.h
@@ -748,6 +748,7 @@ extern int code_copy_enabled;
 #define CPU_INTERRUPT_SMI    0x40 /* (x86 only) SMI interrupt pending */
 #define CPU_INTERRUPT_DEBUG  0x80 /* Debug event occured.  */
 #define CPU_INTERRUPT_VIRQ   0x100 /* virtual interrupt pending.  */
+#define CPU_INTERRUPT_NMI    0x200 /* NMI pending. */
 
 void cpu_interrupt(CPUState *s, int mask);
 void cpu_reset_interrupt(CPUState *env, int mask);
Index: b/cpu-exec.c
===================================================================
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -505,6 +505,12 @@ int cpu_exec(CPUState *env1)
                         env->interrupt_request &= ~CPU_INTERRUPT_SMI;
                         do_smm_enter();
                         BREAK_CHAIN;
+                    } else if ((interrupt_request & CPU_INTERRUPT_NMI) &&
+                        !(env->hflags & HF_NMI_MASK)) {
+                        env->interrupt_request &= ~CPU_INTERRUPT_NMI;
+                        env->hflags |= HF_NMI_MASK;
+                        do_interrupt(EXCP02_NMI, 0, 0, 0, 1);
+                        BREAK_CHAIN;
                     } else if ((interrupt_request & CPU_INTERRUPT_HARD) &&
                         (env->eflags & IF_MASK || env->hflags & HF_HIF_MASK) &&
                         !(env->hflags & HF_INHIBIT_IRQ_MASK)) {
Index: b/target-i386/cpu.h
===================================================================
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -148,6 +148,7 @@
 #define HF_SMM_SHIFT        19 /* CPU in SMM mode */
 #define HF_GIF_SHIFT        20 /* if set CPU takes interrupts */
 #define HF_HIF_SHIFT        21 /* shadow copy of IF_MASK when in SVM */
+#define HF_NMI_SHIFT        22 /* CPU serving NMI */
 
 #define HF_CPL_MASK          (3 << HF_CPL_SHIFT)
 #define HF_SOFTMMU_MASK      (1 << HF_SOFTMMU_SHIFT)
@@ -167,6 +168,7 @@
 #define HF_SMM_MASK          (1 << HF_SMM_SHIFT)
 #define HF_GIF_MASK          (1 << HF_GIF_SHIFT)
 #define HF_HIF_MASK          (1 << HF_HIF_SHIFT)
+#define HF_NMI_MASK          (1 << HF_NMI_SHIFT)
 
 #define CR0_PE_MASK  (1 << 0)
 #define CR0_MP_MASK  (1 << 1)
Index: b/target-i386/helper.c
===================================================================
--- a/target-i386/helper.c
+++ b/target-i386/helper.c
@@ -2382,6 +2382,7 @@ void helper_iret_real(int shift)
     if (shift == 0)
         eflags_mask &= 0xffff;
     load_eflags(new_eflags, eflags_mask);
+    env->hflags &= ~HF_NMI_MASK;
 }
 
 static inline void validate_seg(int seg_reg, int cpl)
@@ -2633,6 +2634,7 @@ void helper_iret_protected(int shift, in
     } else {
         helper_ret_protected(shift, 1, 0);
     }
+    env->hflags &= ~HF_NMI_MASK;
 #ifdef USE_KQEMU
     if (kqemu_is_ok(env)) {
         CC_OP = CC_OP_EFLAGS;