Re: [Xen-devel] Re: [PATCH v2] xen: x86_32: do not enable iterrupts when returning from exception in interrupt context

[Igor Mammedov <imammedo@xxxxxxxxxx>]

On 09/02/2011 03:40 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Sep 02, 2011 at 10:18:23AM +0200, Igor Mammedov wrote:
> > On 09/01/2011 06:46 PM, Jeremy Fitzhardinge wrote:
> > > On 09/01/2011 04:46 AM, Igor Mammedov wrote:
> > > > 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@xxxxxxxxxx>
> > > > Signed-off-by: Jeremy Fitzhardinge<jeremy@xxxxxxxx>
> > > One nit, this should be acked-by or reviewed-by, not signed-off-by,
> > > since the patch isn't passing through my hands.
> > >
> > >      J
> > I'm new to this stuff, would you like me to re-post it?
> That is OK.  I fixed it up in the git commit. Thanks for finding this one!
You're welcome!
I've learned a lot while debugging it. In particular, how to use kvm and qemu's
gdbstub to debug xen and guest using gdb.

--
Thanks,
 Igor

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