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Subject[016/107] xen: x86_32: do not enable iterrupts when returning from exception in interrupt context
2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Igor Mammedov <imammedo@redhat.com>

commit d198d499148a0c64a41b3aba9e7dd43772832b91 upstream.

If vmalloc page_fault happens inside of interrupt handler with interrupts
disabled then on exit path from exception handler when there is no pending
interrupts, the following code (arch/x86/xen/xen-asm_32.S:112):

cmpw $0x0001, XEN_vcpu_info_pending(%eax)
sete XEN_vcpu_info_mask(%eax)

will enable interrupts even if they has been previously disabled according to
eflags from the bounce frame (arch/x86/xen/xen-asm_32.S:99)

testb $X86_EFLAGS_IF>>8, 8+1+ESP_OFFSET(%esp)
setz XEN_vcpu_info_mask(%eax)

Solution is in setting XEN_vcpu_info_mask only when it should be set
according to
cmpw $0x0001, XEN_vcpu_info_pending(%eax)
but not clearing it if there isn't any pending events.

Reproducer for bug is attached to RHBZ 707552

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/x86/xen/xen-asm_32.S | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -113,11 +113,13 @@ xen_iret_start_crit:

/*
* If there's something pending, mask events again so we can
- * jump back into xen_hypervisor_callback
+ * jump back into xen_hypervisor_callback. Otherwise do not
+ * touch XEN_vcpu_info_mask.
*/
- sete XEN_vcpu_info_mask(%eax)
+ jne 1f
+ movb $1, XEN_vcpu_info_mask(%eax)

- popl %eax
+1: popl %eax

/*
* From this point on the registers are restored and the stack



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