x86: only enable interrupts when kernel state has been set up

The sysenter path tries to enable interrupts immediately.  Unfortunately
this doesn't work in a paravirt environment, because not enough kernel
state has been set up at that point (namely, pointing %fs to the kernel
percpu data segment).  To fix this, defer ENABLE_INTERRUPTS until after
the kernel state has been set up.

Unfortunately this means that we're running with interrupts disabled
for a while without calling the IRQ tracing code, but that can't be
called without setting up %fs either.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 9 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 4b87c32b639f..a664d5726d8d 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -291,10 +291,10 @@ ENTRY(ia32_sysenter_target)
         movl TSS_sysenter_sp0(%esp),%esp
 sysenter_past_esp:
         /*
-         * No need to follow this irqs on/off section: the syscall
-         * disabled irqs and here we enable it straight after entry:
+         * Interrupts are disabled here, but we can't trace it until
+         * enough kernel state to call TRACE_IRQS_OFF can be called - but
+         * we immediately enable interrupts at that point anyway.
          */
-        ENABLE_INTERRUPTS(CLBR_NONE)
         pushl $(__USER_DS)
         CFI_ADJUST_CFA_OFFSET 4
         /*CFI_REL_OFFSET ss, 0*/
@@ -302,6 +302,7 @@ sysenter_past_esp:
         CFI_ADJUST_CFA_OFFSET 4
         CFI_REL_OFFSET esp, 0
         pushfl
+        orl $X86_EFLAGS_IF, (%esp)
         CFI_ADJUST_CFA_OFFSET 4
         pushl $(__USER_CS)
         CFI_ADJUST_CFA_OFFSET 4
@@ -315,6 +316,11 @@ sysenter_past_esp:
         CFI_ADJUST_CFA_OFFSET 4
         CFI_REL_OFFSET eip, 0
 
+        pushl %eax
+        CFI_ADJUST_CFA_OFFSET 4
+        SAVE_ALL
+        ENABLE_INTERRUPTS(CLBR_NONE)
+
 /*
  * Load the potential sixth argument from user stack.
  * Careful about security.
@@ -322,14 +328,12 @@ sysenter_past_esp:
         cmpl $__PAGE_OFFSET-3,%ebp
         jae syscall_fault
 1:      movl (%ebp),%ebp
+        movl %ebp,PT_EBP(%esp)
 .section __ex_table,"a"
         .align 4
         .long 1b,syscall_fault
 .previous
 
-        pushl %eax
-        CFI_ADJUST_CFA_OFFSET 4
-        SAVE_ALL
         GET_THREAD_INFO(%ebp)
 
         /* Note, _TIF_SECCOMP is bit number 8, and so it needs testw and not testb */
@@ -543,9 +547,6 @@ END(syscall_exit_work)
 
         RING0_INT_FRAME                 # can't unwind into user space anyway
 syscall_fault:
-        pushl %eax                      # save orig_eax
-        CFI_ADJUST_CFA_OFFSET 4
-        SAVE_ALL
         GET_THREAD_INFO(%ebp)
         movl $-EFAULT,PT_EAX(%esp)
         jmp resume_userspace