Re: Crash in update microcode changes - change set 18475

[Keir Fraser <keir.fraser@eu.citrix.com>]

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The better fix was not to do the update in interrupt context at all, but
instead 'continue' the hypercall on each online processor in turn. This is
what I implemented in c/s 18487. It'd be nice to know that this works for
you (and also for Christoph).

In earlier changesets I've also cleaned up the microcode quite a lot and
reformatted for Xen coding style. My thinking is that microcode-update logic
is not all the complex, and the original code not really all that great, so
I'm not that bothered about keeping closely in sync with the Linux original
version. In this case I'd rather have it in a format I'm happy to hack on
myself.

 -- Keir

On 16/9/08 13:37, "Ross Philipson" <Ross.Philipson@citrix.com> wrote:

> Actually perhaps it is easy to fix. The copying of chunks out of the larger
> microcode buffer seems to just be a convenience. Perhaps just returning offset
> pointers into the original buffer from the get_next_ucode_from_buffer()
> function would get rid of the vmalloc() call. Just a thought as I looked at it
> further.
>  
> Thanks
> Ross
>  
> 
> From: xen-devel-bounces@lists.xensource.com
> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Ross Philipson
> Sent: Monday, September 15, 2008 5:35 PM
> To: xen-devel@lists.xensource.com
> Subject: [Xen-devel] Crash in update microcode changes - change set 18475
>  
> The changes for CPU microcode loading that were done recently (change set
> 18475 in unstable staging) seem to be causing a crash. I am using an Intel
> system and I get an assertion in Xen during the DOM0 boot. This is what I
> believe is going on.
>  
> In xen/arch/x86/microcode.c the routine do_microcode_update() is dispatching
> the update work to each CPU with on_each_cpu() which in turn uses an IPI to
> dispatch the callback vector on each CPU. The microcode update routine passed
> in is called in the IPI context on the target CPU (including irq_enter()
> before calling the ucode function). Within the ucode function the calls
> eventually get down to the Intel specific calls in microcode_intel.c.
> Specifically:
>  
> do_microcode_update_one()
>     microcode_update_cpu()
>            cpu_request_microcode()
>                get_next_ucode_from_buffer()
>  
> Within the last call, vmalloc() is called and eventually _xmalloc() asserts on
> ASSERT(!in_irq()). I checked and the earlier code, though it dispatched work
> to different CPUs with IPIs, did not try to dynamically allocate memory. I am
> not sure how to fix this easily without redoing how the whole new microcode
> framework works. Also I didn¹t look closely at AMD but it may have the same
> issue. I can take a crack at fixing it but maybe someone will see a simple
> solution.
>  
> Thanks
> Ross
>  
> Ross Philipson
> Senior Software Engineer
> Citrix Systems, Inc
> 14 Crosby Drive
> Bedford, MA 01730
> 781-301-7949
> ross.philipson@citrix.com
>  
> 
> 
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> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel



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