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-rw-r--r--arch/i386/kernel/entry.S71
1 files changed, 71 insertions, 0 deletions
diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 3c3c220488c..ffb23654427 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -1023,6 +1023,77 @@ ENTRY(kernel_thread_helper)
CFI_ENDPROC
ENDPROC(kernel_thread_helper)
+#ifdef CONFIG_XEN
+ENTRY(xen_hypervisor_callback)
+ CFI_STARTPROC
+ pushl $0
+ CFI_ADJUST_CFA_OFFSET 4
+ SAVE_ALL
+ TRACE_IRQS_OFF
+ mov %esp, %eax
+ call xen_evtchn_do_upcall
+ jmp ret_from_intr
+ CFI_ENDPROC
+ENDPROC(xen_hypervisor_callback)
+
+# Hypervisor uses this for application faults while it executes.
+# We get here for two reasons:
+# 1. Fault while reloading DS, ES, FS or GS
+# 2. Fault while executing IRET
+# Category 1 we fix up by reattempting the load, and zeroing the segment
+# register if the load fails.
+# Category 2 we fix up by jumping to do_iret_error. We cannot use the
+# normal Linux return path in this case because if we use the IRET hypercall
+# to pop the stack frame we end up in an infinite loop of failsafe callbacks.
+# We distinguish between categories by maintaining a status value in EAX.
+ENTRY(xen_failsafe_callback)
+ CFI_STARTPROC
+ pushl %eax
+ CFI_ADJUST_CFA_OFFSET 4
+ movl $1,%eax
+1: mov 4(%esp),%ds
+2: mov 8(%esp),%es
+3: mov 12(%esp),%fs
+4: mov 16(%esp),%gs
+ testl %eax,%eax
+ popl %eax
+ CFI_ADJUST_CFA_OFFSET -4
+ lea 16(%esp),%esp
+ CFI_ADJUST_CFA_OFFSET -16
+ jz 5f
+ addl $16,%esp
+ jmp iret_exc # EAX != 0 => Category 2 (Bad IRET)
+5: pushl $0 # EAX == 0 => Category 1 (Bad segment)
+ CFI_ADJUST_CFA_OFFSET 4
+ SAVE_ALL
+ jmp ret_from_exception
+ CFI_ENDPROC
+
+.section .fixup,"ax"
+6: xorl %eax,%eax
+ movl %eax,4(%esp)
+ jmp 1b
+7: xorl %eax,%eax
+ movl %eax,8(%esp)
+ jmp 2b
+8: xorl %eax,%eax
+ movl %eax,12(%esp)
+ jmp 3b
+9: xorl %eax,%eax
+ movl %eax,16(%esp)
+ jmp 4b
+.previous
+.section __ex_table,"a"
+ .align 4
+ .long 1b,6b
+ .long 2b,7b
+ .long 3b,8b
+ .long 4b,9b
+.previous
+ENDPROC(xen_failsafe_callback)
+
+#endif /* CONFIG_XEN */
+
.section .rodata,"a"
#include "syscall_table.S"