x86: Assert !in_atomic() before exiting to guest context.

Signed-off-by: Keir Fraser <keir@xen.org>

xen/arch/x86/hvm/svm/entry.S

@@ -42,6 +42,7 @@
 ENTRY(svm_asm_do_resume)
         call svm_intr_assist
         call_with_regs(nsvm_vcpu_switch)
+        ASSERT_NOT_IN_ATOMIC
 
         get_current(bx)
         CLGI

xen/arch/x86/hvm/vmx/entry.S

@@ -98,6 +98,7 @@ vmx_asm_vmexit_handler:
 vmx_asm_do_vmentry:
         call vmx_intr_assist
         call nvmx_switch_guest
+        ASSERT_NOT_IN_ATOMIC
 
         get_current(bx)
         cli

xen/arch/x86/x86_64/compat/entry.S

@@ -92,6 +92,7 @@ compat_skip_clobber:
 
 /* %rbx: struct vcpu */
 ENTRY(compat_test_all_events)
+        ASSERT_NOT_IN_ATOMIC
         cli                             # tests must not race interrupts
 /*compat_test_softirqs:*/
         movl  VCPU_processor(%rbx),%eax

xen/arch/x86/x86_64/entry.S

@@ -190,6 +190,7 @@ skip_clobber:
 
 /* %rbx: struct vcpu */
 test_all_events:
+        ASSERT_NOT_IN_ATOMIC
         cli                             # tests must not race interrupts
 /*test_softirqs:*/  
         movl  VCPU_processor(%rbx),%eax

xen/common/preempt.c

@@ -30,3 +30,9 @@ bool_t in_atomic(void)
 {
     return preempt_count() || in_irq() || !local_irq_is_enabled();
 }
+
+/* asm helper */
+void bug_if_in_atomic(void)
+{
+    BUG_ON(in_atomic());
+}

xen/include/asm-x86/asm_defns.h

@@ -59,6 +59,14 @@ void ret_from_intr(void);
         GET_STACK_BASE(reg);                      \
         __GET_CURRENT(reg)
 
+#ifndef NDEBUG
+#define ASSERT_NOT_IN_ATOMIC                                             \
+    sti; /* sometimes called with interrupts disabled: safe to enable */ \
+    call bug_if_in_atomic
+#else
+#define ASSERT_NOT_IN_ATOMIC
+#endif
+
 #endif
 
 #endif /* __X86_ASM_DEFNS_H__ */