xen: x86_32: do not enable iterrupts when returning from exception in interrupt context
authorIgor Mammedov <imammedo@redhat.com>
Thu, 1 Sep 2011 11:46:55 +0000 (13:46 +0200)
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Thu, 1 Sep 2011 16:54:42 +0000 (12:54 -0400)
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

CC: stable@kernel.org
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>
arch/x86/xen/xen-asm_32.S

index 22a2093b58623cca3472a03c3950cad4395a884d..b040b0e518caf0a0fe382999b36c2c04e7344860 100644 (file)
@@ -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