[PATCH 25 of 31] x86: only enable interrupts when kernel state has been set up

[Jeremy Fitzhardinge <jeremy@goop.org>]

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>
---
 arch/x86/kernel/entry_32.S |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -290,10 +290,10 @@
 	movl TSS_sysenter_sp0(%esp),%esp
 ENTRY(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*/
@@ -329,6 +329,7 @@
 	pushl %eax
 	CFI_ADJUST_CFA_OFFSET 4
 	SAVE_ALL
+	ENABLE_INTERRUPTS(CLBR_NONE)
 	GET_THREAD_INFO(%ebp)
 
 	/* Note, _TIF_SECCOMP is bit number 8, and so it needs testw and not testb */
@@ -545,6 +546,7 @@
 	pushl %eax			# save orig_eax
 	CFI_ADJUST_CFA_OFFSET 4
 	SAVE_ALL
+	ENABLE_INTERRUPTS(CLBR_NONE)
 	GET_THREAD_INFO(%ebp)
 	movl $-EFAULT,PT_EAX(%esp)
 	jmp resume_userspace