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RE: [Xen-devel] RE: odd IRQ behavior

To: "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] RE: odd IRQ behavior
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Sun, 1 Mar 2009 21:48:38 +0800
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Thread-topic: [Xen-devel] RE: odd IRQ behavior
>From: Cihula, Joseph
>Sent: Saturday, February 28, 2009 2:55 AM
>> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>> Sent: Friday, February 27, 2009 7:42 AM
>> On 27/02/2009 14:35, "Cihula, Joseph" 
><joseph.cihula@xxxxxxxxx> wrote:
>> >> Please provide some backtraces.
>> >>
>> >>  -- Keir
>> >
>> > Trace of assertion at shutdown entry:
>> Okay, the ASSERT(!in_irq()) crash on shutdown is due to 
>having IPIed to the
>> BP to make it drive the shutdown. Hence the BP is actually 
>in IRQ context.
>> If you then zero the IRQ counter, it will get decremented on 
>exit from the
>> shutdown code (and the IPI interrupt) on S3 resume... Except 
>I'm confused by
>> this because machine_restart() is not used for S3 suspend/resume. So
>> actually I'm not sure how you end up in IRQ context on S3 
>suspend, and you
>> didn't send a backtrace of that situation. To get to the BP 
>on S3 suspend we
>> use continue_hypercall_on_cpu(), which does not leave us in 
>IRQ context.
>> For the check_lock() assertion, either do not local_irq_disable() in
>> tboot_shutdown() (is that needed?) or perhaps even better 
>(solves all the
>> crashes you've seen) why not disable paging before jumping 
>into tboot and
>> hence avoid needing map_pages_to_xen()? I can't see why 
>tboot would care to
>> run on our random pagetables, and implementing a stub to 
>jump into / out of
>> non-paged mode would be very easy. I can explain more how to 
>do this if this
>> is a suitable solution. Another alternative would be to map 
>tboot pages
>> during boot and leave them mapped forever after. That also 
>would avoid these
>> map_pages_to_xen() during S3/shutdown issues, and I suppose 
>is easier than
>> implementing a return-to-no-paging stub.
>On S3, we also need to create integrity measurements for the 
>xenheap and domheap, which require mapping pages.  So I don't 
>think that either moving the 1:1 mapping early or the disable 
>paging would solve the problem (it would just shift it).
>I think that I did find a way to avoid the reboot spinlock 
>BUG_ON by using spin_debug_{disable/enable}().  S3 still isn't 
>working, but I haven't been able to track down why yet 
>(unfortunately, serial output stops before it fails).

Just be caution that current Xen upstream has several S3 bugs
which was fixed by Guanqun but not checked in yet. Maybe you
can have a try by http://markmail.org/thread/fkcowjzdbqq3qbjp
to avoid hunting same issues.


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