Hm. I think the problem was that the patch changed the ordering so that
the %ebp fault test was happening with interrupts disabled, meaning that
any fault-in would happen with interrupts disabled.
Could you tell me if this revised patch still provokes a problem?
Thanks,
J
Subject: 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>
---
arch/x86/kernel/entry_32.S | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
===================================================================
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -290,10 +290,10 @@ ENTRY(ia32_sysenter_target)
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*/
@@ -314,6 +314,11 @@ ENTRY(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.
@@ -321,14 +326,12 @@ ENTRY(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 */
@@ -542,9 +545,6 @@ 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
--
