1.1 --- a/linux-2.6.9-xen-sparse/arch/xen/i386/kernel/entry.S	Fri Nov 26 18:24:37 2004 +0000
     1.2 +++ b/linux-2.6.9-xen-sparse/arch/xen/i386/kernel/entry.S	Sat Nov 27 13:17:36 2004 +0000
     1.3 @@ -64,6 +64,7 @@ ES		= 0x20
     1.4  ORIG_EAX	= 0x24
     1.5  EIP		= 0x28
     1.6  CS		= 0x2C
     1.7 +EVENT_MASK	= 0x2E
     1.8  EFLAGS		= 0x30
     1.9  OLDESP		= 0x34
    1.10  OLDSS		= 0x38
    1.11 @@ -91,23 +92,16 @@ VM_MASK		= 0x00020000
    1.12  
    1.13  #define XEN_BLOCK_EVENTS(reg)	movb $1,evtchn_upcall_mask(reg)
    1.14  #define XEN_UNBLOCK_EVENTS(reg)	movb $0,evtchn_upcall_mask(reg)
    1.15 -#define XEN_TEST_PENDING(reg)	testb $0x1,evtchn_upcall_pending(reg)
    1.16 +#define XEN_TEST_PENDING(reg)	testb $0xFF,evtchn_upcall_pending(reg)
    1.17  
    1.18  #ifdef CONFIG_PREEMPT
    1.19 -#ifdef CONFIG_SMP
    1.20 -#define preempt_stop		GET_THREAD_INFO(%ebp)			; \
    1.21 -				XEN_GET_VCPU_INFO(%esi)			; \
    1.22 -				XEN_BLOCK_EVENTS(%esi)
    1.23 -#else
    1.24 -#define preempt_stop		XEN_GET_VCPU_INFO(%esi)			; \
    1.25 -				XEN_BLOCK_EVENTS(%esi)
    1.26 -#endif
    1.27 +#define preempt_stop		XEN_BLOCK_EVENTS(%esi)
    1.28  #else
    1.29  #define preempt_stop
    1.30  #define resume_kernel		restore_all
    1.31  #endif
    1.32  
    1.33 -#define SAVE_ALL \
    1.34 +#define SAVE_ALL_NO_EVENTMASK \
    1.35  	cld; \
    1.36  	pushl %es; \
    1.37  	pushl %ds; \
    1.38 @@ -120,7 +114,13 @@ VM_MASK		= 0x00020000
    1.39  	pushl %ebx; \
    1.40  	movl $(__USER_DS), %edx; \
    1.41  	movl %edx, %ds; \
    1.42 -	movl %edx, %es;
    1.43 +	movl %edx, %es
    1.44 +
    1.45 +#define SAVE_ALL \
    1.46 +	SAVE_ALL_NO_EVENTMASK; \
    1.47 +	XEN_GET_VCPU_INFO(%esi); \
    1.48 +	movb evtchn_upcall_mask(%esi), %dl; \
    1.49 +	movb %dl, EVENT_MASK(%esp)
    1.50  
    1.51  #define RESTORE_INT_REGS \
    1.52  	popl %ebx;	\
    1.53 @@ -224,35 +224,30 @@ ret_from_intr:
    1.54  	testl $(VM_MASK | 2), %eax
    1.55  	jz resume_kernel		# returning to kernel or vm86-space
    1.56  ENTRY(resume_userspace)
    1.57 -	XEN_GET_VCPU_INFO(%esi)
    1.58 -	XEN_BLOCK_EVENTS(%esi)		# make tests atomic
    1.59 -					# make sure we don't miss an interrupt
    1.60 +	XEN_BLOCK_EVENTS(%esi)		# make sure we don't miss an interrupt
    1.61  					# setting need_resched or sigpending
    1.62  					# between sampling and the iret
    1.63 -ret_syscall_tests:
    1.64  	movl TI_flags(%ebp), %ecx
    1.65  	andl $_TIF_WORK_MASK, %ecx	# is there any work to be done on
    1.66  					# int/exception return?
    1.67  	jne work_pending
    1.68 -	jmp restore_all_enable_events
    1.69 +	jmp restore_all
    1.70  
    1.71  #ifdef CONFIG_PREEMPT
    1.72  ENTRY(resume_kernel)
    1.73 -	XEN_GET_VCPU_INFO(%esi)
    1.74  	cmpl $0,TI_preempt_count(%ebp)	# non-zero preempt_count ?
    1.75 -	jnz restore_all_enable_events
    1.76 +	jnz restore_all
    1.77  need_resched:
    1.78  	movl TI_flags(%ebp), %ecx	# need_resched set ?
    1.79  	testb $_TIF_NEED_RESCHED, %cl
    1.80 -	jz restore_all_enable_events
    1.81 +	jz restore_all
    1.82  	testl $IF_MASK,EFLAGS(%esp)     # interrupts off (exception path) ?
    1.83 -	jz restore_all_enable_events
    1.84 +	jz restore_all
    1.85  	movl $PREEMPT_ACTIVE,TI_preempt_count(%ebp)
    1.86 -	XEN_UNBLOCK_EVENTS(%esi)	# reenable event callbacks
    1.87 +	XEN_UNBLOCK_EVENTS(%esi)
    1.88  	call schedule
    1.89  	movl $0,TI_preempt_count(%ebp)
    1.90 -	XEN_GET_VCPU_INFO(%esi)
    1.91 -	XEN_BLOCK_EVENTS(%esi)		# make tests atomic
    1.92 +	XEN_BLOCK_EVENTS(%esi)
    1.93  	jmp need_resched
    1.94  #endif
    1.95  
    1.96 @@ -285,11 +280,11 @@ 1:	movl (%ebp),%ebp
    1.97  	pushl %eax
    1.98  	SAVE_ALL
    1.99  	GET_THREAD_INFO(%ebp)
   1.100 -	cmpl $(nr_syscalls), %eax
   1.101 -	jae syscall_badsys
   1.102  
   1.103  	testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT),TI_flags(%ebp)
   1.104  	jnz syscall_trace_entry
   1.105 +	cmpl $(nr_syscalls), %eax
   1.106 +	jae syscall_badsys
   1.107  	call *sys_call_table(,%eax,4)
   1.108  	movl %eax,EAX(%esp)
   1.109  	cli
   1.110 @@ -308,48 +303,43 @@ ENTRY(system_call)
   1.111  	pushl %eax			# save orig_eax
   1.112  	SAVE_ALL
   1.113  	GET_THREAD_INFO(%ebp)
   1.114 -	cmpl $(nr_syscalls), %eax
   1.115 -	jae syscall_badsys
   1.116  					# system call tracing in operation
   1.117  	testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT),TI_flags(%ebp)
   1.118  	jnz syscall_trace_entry
   1.119 +	cmpl $(nr_syscalls), %eax
   1.120 +	jae syscall_badsys
   1.121  syscall_call:
   1.122  	call *sys_call_table(,%eax,4)
   1.123  	movl %eax,EAX(%esp)		# store the return value
   1.124  syscall_exit:
   1.125 -	XEN_GET_VCPU_INFO(%esi)
   1.126 -	XEN_BLOCK_EVENTS(%esi)		# make tests atomic
   1.127 -					# make sure we don't miss an interrupt
   1.128 +	XEN_BLOCK_EVENTS(%esi)		# make sure we don't miss an interrupt
   1.129  					# setting need_resched or sigpending
   1.130  					# between sampling and the iret
   1.131  	movl TI_flags(%ebp), %ecx
   1.132  	testw $_TIF_ALLWORK_MASK, %cx	# current->work
   1.133  	jne syscall_exit_work
   1.134 -	jmp restore_all_enable_events
   1.135 -
   1.136 -	ALIGN
   1.137  restore_all:
   1.138 +	movb EVENT_MASK(%esp), %al
   1.139 +	notb %al			# %al == ~saved_mask
   1.140 +	andb evtchn_upcall_mask(%esi),%al
   1.141 +	andb $1,%al			# %al == mask & ~saved_mask
   1.142 +	jnz restore_all_enable_events	#     != 0 => reenable event delivery
   1.143  	RESTORE_ALL
   1.144  
   1.145  	# perform work that needs to be done immediately before resumption
   1.146  	ALIGN
   1.147  work_pending:
   1.148 -	XEN_UNBLOCK_EVENTS(%esi)	# reenable event callbacks
   1.149  	testb $_TIF_NEED_RESCHED, %cl
   1.150  	jz work_notifysig
   1.151  work_resched:
   1.152  	call schedule
   1.153 -	XEN_GET_VCPU_INFO(%esi)
   1.154 -	XEN_BLOCK_EVENTS(%esi)		# make tests atomic
   1.155 -					# make sure we don't miss an interrupt
   1.156 +	XEN_BLOCK_EVENTS(%esi)		# make sure we don't miss an interrupt
   1.157  					# setting need_resched or sigpending
   1.158  					# between sampling and the iret
   1.159  	movl TI_flags(%ebp), %ecx
   1.160  	andl $_TIF_WORK_MASK, %ecx	# is there any work to be done other
   1.161  					# than syscall tracing?
   1.162 -	jz restore_all_enable_events
   1.163 -	# XXXcl sti missing???
   1.164 -	XEN_UNBLOCK_EVENTS(%esi)	# reenable event callbacks
   1.165 +	jz restore_all
   1.166  	testb $_TIF_NEED_RESCHED, %cl
   1.167  	jnz work_resched
   1.168  
   1.169 @@ -361,8 +351,7 @@ work_notifysig:				# deal with pending s
   1.170  					# vm86-space
   1.171  	xorl %edx, %edx
   1.172  	call do_notify_resume
   1.173 -	XEN_GET_VCPU_INFO(%esi)
   1.174 -	jmp restore_all_enable_events
   1.175 +	jmp restore_all
   1.176  
   1.177  	ALIGN
   1.178  work_notifysig_v86:
   1.179 @@ -372,8 +361,7 @@ work_notifysig_v86:
   1.180  	movl %eax, %esp
   1.181  	xorl %edx, %edx
   1.182  	call do_notify_resume
   1.183 -	XEN_GET_VCPU_INFO(%esi)
   1.184 -	jmp restore_all_enable_events
   1.185 +	jmp restore_all
   1.186  
   1.187  	# perform syscall exit tracing
   1.188  	ALIGN
   1.189 @@ -390,11 +378,9 @@ syscall_trace_entry:
   1.190  	# perform syscall exit tracing
   1.191  	ALIGN
   1.192  syscall_exit_work:
   1.193 -	XEN_GET_VCPU_INFO(%esi)
   1.194 -	testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT), %cl
   1.195 +	testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP), %cl
   1.196  	jz work_pending
   1.197 -	XEN_UNBLOCK_EVENTS(%esi)	# reenable event callbacks
   1.198 -					# could let do_syscall_trace() call
   1.199 +	XEN_UNBLOCK_EVENTS(%esi)	# could let do_syscall_trace() call
   1.200  					# schedule() instead
   1.201  	movl %esp, %eax
   1.202  	movl $1, %edx
   1.203 @@ -414,6 +400,44 @@ syscall_badsys:
   1.204  	movl $-ENOSYS,EAX(%esp)
   1.205  	jmp resume_userspace
   1.206  
   1.207 +#if 0 /* XEN */
   1.208 +/*
   1.209 + * Build the entry stubs and pointer table with
   1.210 + * some assembler magic.
   1.211 + */
   1.212 +.data
   1.213 +ENTRY(interrupt)
   1.214 +.text
   1.215 +
   1.216 +vector=0
   1.217 +ENTRY(irq_entries_start)
   1.218 +.rept NR_IRQS
   1.219 +	ALIGN
   1.220 +1:	pushl $vector-256
   1.221 +	jmp common_interrupt
   1.222 +.data
   1.223 +	.long 1b
   1.224 +.text
   1.225 +vector=vector+1
   1.226 +.endr
   1.227 +
   1.228 +	ALIGN
   1.229 +common_interrupt:
   1.230 +	SAVE_ALL
   1.231 +	call do_IRQ
   1.232 +	jmp ret_from_intr
   1.233 +
   1.234 +#define BUILD_INTERRUPT(name, nr)	\
   1.235 +ENTRY(name)				\
   1.236 +	pushl $nr-256;			\
   1.237 +	SAVE_ALL			\
   1.238 +	call smp_/**/name;	\
   1.239 +	jmp ret_from_intr;
   1.240 +
   1.241 +/* The include is where all of the SMP etc. interrupts come from */
   1.242 +#include "entry_arch.h"
   1.243 +#endif /* XEN */
   1.244 +
   1.245  ENTRY(divide_error)
   1.246  	pushl $0			# no error code
   1.247  	pushl $do_divide_error
   1.248 @@ -438,9 +462,12 @@ error_code:
   1.249  	movl %esp, %edx
   1.250  	pushl %esi			# push the error code
   1.251  	pushl %edx			# push the pt_regs pointer
   1.252 -	movl $(__KERNEL_DS), %edx	# XXXcl USER?
   1.253 +	movl $(__USER_DS), %edx
   1.254  	movl %edx, %ds
   1.255  	movl %edx, %es
   1.256 +	XEN_GET_VCPU_INFO(%esi)
   1.257 +	movb evtchn_upcall_mask(%esi), %dl
   1.258 +	movb %dl, EVENT_MASK+8(%esp)
   1.259  	call *%edi
   1.260  	addl $8, %esp
   1.261  	jmp ret_from_exception
   1.262 @@ -458,22 +485,22 @@ error_code:
   1.263  # activation and restart the handler using the previous one.
   1.264  ENTRY(hypervisor_callback)
   1.265  	pushl %eax
   1.266 -	SAVE_ALL
   1.267 -	GET_THREAD_INFO(%ebp)
   1.268 +	SAVE_ALL_NO_EVENTMASK
   1.269  	movl EIP(%esp),%eax
   1.270  	cmpl $scrit,%eax
   1.271  	jb   11f
   1.272  	cmpl $ecrit,%eax
   1.273  	jb   critical_region_fixup
   1.274 -11:	push %esp
   1.275 +11:	XEN_GET_VCPU_INFO(%esi)
   1.276 +	movb $0, EVENT_MASK(%esp)
   1.277 +	push %esp
   1.278  	call evtchn_do_upcall
   1.279  	add  $4,%esp
   1.280 -	XEN_GET_VCPU_INFO(%esi)
   1.281 -	movb CS(%esp),%cl
   1.282 -	test $2,%cl			# slow return to ring 2 or 3
   1.283 -	jne  ret_syscall_tests
   1.284 +	jmp  ret_from_intr
   1.285 +
   1.286 +        ALIGN
   1.287  restore_all_enable_events:  
   1.288 -safesti:XEN_UNBLOCK_EVENTS(%esi)	# reenable event callbacks
   1.289 +	XEN_UNBLOCK_EVENTS(%esi)
   1.290  scrit:	/**** START OF CRITICAL REGION ****/
   1.291  	XEN_TEST_PENDING(%esi)
   1.292  	jnz  14f			# process more events if necessary...
   1.293 @@ -599,11 +626,18 @@ ENTRY(debug)
   1.294  	jne debug_stack_correct
   1.295  	FIX_STACK(12, debug_stack_correct, debug_esp_fix_insn)
   1.296  debug_stack_correct:
   1.297 -	pushl $0
   1.298 -	pushl $do_debug
   1.299 -	jmp error_code
   1.300 +	pushl $-1			# mark this as an int
   1.301 +	SAVE_ALL
   1.302 +	movl %esp,%edx
   1.303 +  	pushl $0
   1.304 +	pushl %edx
   1.305 +	call do_debug
   1.306 +	addl $8,%esp
   1.307 +	testl %eax,%eax
   1.308 +	jnz restore_all
   1.309 +	jmp ret_from_exception
   1.310  
   1.311 -#if 0
   1.312 +#if 0 /* XEN */
   1.313  /*
   1.314   * NMI is doubly nasty. It can happen _while_ we're handling
   1.315   * a debug fault, and the debug fault hasn't yet been able to
   1.316 @@ -649,12 +683,19 @@ nmi_debug_stack_check:
   1.317  nmi_debug_stack_fixup:
   1.318  	FIX_STACK(24,nmi_stack_correct, 1)
   1.319  	jmp nmi_stack_correct
   1.320 -#endif
   1.321 +#endif /* XEN */
   1.322  
   1.323  ENTRY(int3)
   1.324 +	pushl $-1			# mark this as an int
   1.325 +	SAVE_ALL
   1.326 +	movl %esp,%edx
   1.327  	pushl $0
   1.328 -	pushl $do_int3
   1.329 -	jmp error_code
   1.330 +	pushl %edx
   1.331 +	call do_int3
   1.332 +	addl $8,%esp
   1.333 +	testl %eax,%eax
   1.334 +	jnz restore_all
   1.335 +	jmp ret_from_exception
   1.336  
   1.337  ENTRY(overflow)
   1.338  	pushl $0
   1.339 @@ -676,10 +717,6 @@ ENTRY(coprocessor_segment_overrun)
   1.340  	pushl $do_coprocessor_segment_overrun
   1.341  	jmp error_code
   1.342  
   1.343 -ENTRY(double_fault)
   1.344 -	pushl $do_double_fault
   1.345 -	jmp error_code
   1.346 -
   1.347  ENTRY(invalid_TSS)
   1.348  	pushl $do_invalid_TSS
   1.349  	jmp error_code
   1.350 @@ -702,36 +739,37 @@ ENTRY(alignment_check)
   1.351  
   1.352  # This handler is special, because it gets an extra value on its stack,
   1.353  # which is the linear faulting address.
   1.354 -#define PAGE_FAULT_STUB(_name1, _name2)					  \
   1.355 -ENTRY(_name1)								  \
   1.356 -	pushl %ds							; \
   1.357 -	pushl %eax							; \
   1.358 -	xorl %eax,%eax							; \
   1.359 -	pushl %ebp							; \
   1.360 -	pushl %edi							; \
   1.361 -	pushl %esi							; \
   1.362 -	pushl %edx							; \
   1.363 -	decl %eax			/* eax = -1 */			; \
   1.364 -	pushl %ecx							; \
   1.365 -	pushl %ebx							; \
   1.366 -	GET_THREAD_INFO(%ebp)						; \
   1.367 -	cld								; \
   1.368 -	movl %es,%ecx							; \
   1.369 -	movl ORIG_EAX(%esp), %esi	/* get the error code */	; \
   1.370 -	movl ES(%esp), %edi		/* get the faulting address */	; \
   1.371 -	movl %eax, ORIG_EAX(%esp)					; \
   1.372 -	movl %ecx, ES(%esp)						; \
   1.373 -	movl %esp,%edx							; \
   1.374 -	pushl %edi			/* push the faulting address */	; \
   1.375 -	pushl %esi			/* push the error code */	; \
   1.376 -	pushl %edx			/* push the pt_regs pointer */	; \
   1.377 -	movl $(__KERNEL_DS),%edx					; \
   1.378 -	movl %edx,%ds							; \
   1.379 -	movl %edx,%es							; \
   1.380 -	call _name2							; \
   1.381 -	addl $12,%esp							; \
   1.382 -	jmp ret_from_exception						;
   1.383 -PAGE_FAULT_STUB(page_fault, do_page_fault)
   1.384 +ENTRY(page_fault)
   1.385 +	pushl %ds
   1.386 +	pushl %eax
   1.387 +	xorl %eax,%eax
   1.388 +	pushl %ebp
   1.389 +	pushl %edi
   1.390 +	pushl %esi
   1.391 +	pushl %edx
   1.392 +	decl %eax			/* eax = -1 */
   1.393 +	pushl %ecx
   1.394 +	pushl %ebx
   1.395 +	GET_THREAD_INFO(%ebp)
   1.396 +	cld
   1.397 +	movl %es,%ecx
   1.398 +	movl ORIG_EAX(%esp), %esi	/* get the error code */
   1.399 +	movl ES(%esp), %edi		/* get the faulting address */
   1.400 +	movl %eax, ORIG_EAX(%esp)
   1.401 +	movl %ecx, ES(%esp)
   1.402 +	movl %esp,%edx
   1.403 +	pushl %edi			/* push the faulting address */
   1.404 +	pushl %esi			/* push the error code */
   1.405 +	pushl %edx			/* push the pt_regs pointer */
   1.406 +	movl $(__KERNEL_DS),%edx
   1.407 +	movl %edx,%ds
   1.408 +	movl %edx,%es
   1.409 +	XEN_GET_VCPU_INFO(%esi)
   1.410 +	movb evtchn_upcall_mask(%esi), %dl
   1.411 +	movb %dl, EVENT_MASK+12(%esp)
   1.412 +	call do_page_fault
   1.413 +	addl $12,%esp
   1.414 +	jmp ret_from_exception
   1.415  
   1.416  #ifdef CONFIG_X86_MCE
   1.417  ENTRY(machine_check)
   1.418 @@ -1030,5 +1068,6 @@ ENTRY(sys_call_table)
   1.419  	.long sys_mq_notify
   1.420  	.long sys_mq_getsetattr
   1.421  	.long sys_ni_syscall		/* reserved for kexec */
   1.422 +	.long sys_waitid
   1.423  
   1.424  syscall_table_size=(.-sys_call_table)

     2.1 --- a/linux-2.6.9-xen-sparse/arch/xen/i386/kernel/traps.c	Fri Nov 26 18:24:37 2004 +0000
     2.2 +++ b/linux-2.6.9-xen-sparse/arch/xen/i386/kernel/traps.c	Sat Nov 27 13:17:36 2004 +0000
     2.3 @@ -78,7 +78,6 @@ asmlinkage void overflow(void);
     2.4  asmlinkage void bounds(void);
     2.5  asmlinkage void invalid_op(void);
     2.6  asmlinkage void device_not_available(void);
     2.7 -asmlinkage void double_fault(void);
     2.8  asmlinkage void coprocessor_segment_overrun(void);
     2.9  asmlinkage void invalid_TSS(void);
    2.10  asmlinkage void segment_not_present(void);
    2.11 @@ -470,7 +469,6 @@ DO_VM86_ERROR( 4, SIGSEGV, "overflow", o
    2.12  DO_VM86_ERROR( 5, SIGSEGV, "bounds", bounds)
    2.13  DO_ERROR_INFO( 6, SIGILL,  "invalid operand", invalid_op, ILL_ILLOPN, regs->eip)
    2.14  DO_VM86_ERROR( 7, SIGSEGV, "device not available", device_not_available)
    2.15 -DO_ERROR( 8, SIGSEGV, "double fault", double_fault)
    2.16  DO_ERROR( 9, SIGFPE,  "coprocessor segment overrun", coprocessor_segment_overrun)
    2.17  DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
    2.18  DO_ERROR(11, SIGBUS,  "segment not present", segment_not_present)
    2.19 @@ -1032,7 +1030,6 @@ static trap_info_t trap_table[] = {
    2.20  	{  5, 3, __KERNEL_CS, (unsigned long)bounds			},
    2.21  	{  6, 0, __KERNEL_CS, (unsigned long)invalid_op			},
    2.22  	{  7, 0, __KERNEL_CS, (unsigned long)device_not_available	},
    2.23 -	{  8, 0, __KERNEL_CS, (unsigned long)double_fault		},
    2.24  	{  9, 0, __KERNEL_CS, (unsigned long)coprocessor_segment_overrun },
    2.25  	{ 10, 0, __KERNEL_CS, (unsigned long)invalid_TSS		},
    2.26  	{ 11, 0, __KERNEL_CS, (unsigned long)segment_not_present	},

     3.1 --- a/xen/arch/x86/x86_32/entry.S	Fri Nov 26 18:24:37 2004 +0000
     3.2 +++ b/xen/arch/x86/x86_32/entry.S	Sat Nov 27 13:17:36 2004 +0000
     3.3 @@ -339,7 +339,7 @@ error_code:
     3.4          SET_XEN_SEGMENTS(a)
     3.5          testb $X86_EFLAGS_IF>>8,XREGS_eflags+1(%esp)
     3.6          jz    exception_with_ints_disabled
     3.7 -        sti                             # re-enable interrupts
     3.8 +1:      sti                             # re-enable interrupts
     3.9          xorl  %eax,%eax
    3.10          movw  XREGS_entry_vector(%esp),%ax
    3.11          movl  %esp,%edx
    3.12 @@ -354,8 +354,8 @@ error_code:
    3.13  
    3.14  exception_with_ints_disabled:
    3.15          movb  XREGS_cs(%esp),%al
    3.16 -	testb $3,%al                    # interrupts disabled outside Xen?
    3.17 -	jnz   FATAL_exception_with_ints_disabled
    3.18 +	testb $3,%al   # interrupts disabled outside Xen?
    3.19 +	jnz   1b       # it really does happen! (e.g., DOM0 X server)
    3.20          pushl XREGS_eip(%esp)
    3.21          call  search_pre_exception_table
    3.22          addl  $4,%esp