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

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Message-ID: <4E60E1BF.2020206@redhat.com>
Date:	Fri, 02 Sep 2011 16:01:35 +0200
From:	Igor Mammedov <imammedo@...hat.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] Re: [PATCH v2] xen: x86_32: do not enable iterrupts
 when returning from exception in interrupt context

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@...hat.com>
>>>> Signed-off-by: Jeremy Fitzhardinge<jeremy@...p.org>
>>>
>>> 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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