Re: [Xen-devel] 2.6.32.27 dom0 + latest xen staging boot failure

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 02/10/2011 05:03 PM, Kay, Allen M wrote:
> Konrad/Stefano,
>
> Getting back to the xen/dom0 boot failure on my Sandybridge SDP I reported a 
> few weeks ago.
>
> I finally got around to narrow down the problem the call to 
> xen_add_extra_mem() in arch/x86/xen/setup.c/xen_memory_setup().  This call 
> increase the top of E820 memory in dom0 beyond what is actually available.
>
> Before xen_add_extra_mem() is called, the last entry of dom0 e820 table is:
>
>     0000000100000000 - 000000016b45a000 (usable)
>
> After xen_add_extra_mem() is called, the last entry of dom0 e820 table 
> becomes:
>
>     0000000100000000 - 000000023a6f4000 (usable)
>
> This pushes the top of RAM beyond what was reported by Xen's e820 table, 
> which is:
>
> (XEN)  0000000100000000 - 00000001de600000 (usable)
>
> AFAICT, the failure is caused by dom0 accessing non-existent physical memory. 
>  The failure went away after I removed the call to xen_add_extra_mem().

That "extra memory" stuff is reserving some physical address space for
ballooning.  It should be completely unused (and unbacked by any pages)
until the balloon driver populates it; it is reserved memory in the
meantime.

How is that memory getting referenced in your case?

> Another potential problem I noticed with e820 processing is that there is a 
> discrepancy between how Xen processes e820 and how dom0 does it.  In Xen 
> (arch/x86/setup.c/start_xen()), e820 entries are aligned on 
> L2_PAGETABLE_SHIFT boundary while dom0 e820 code does not.  As a result, one 
> of my e820 entry that is 1 page in size got dropped by Xen but got picked up 
> in dom0.  This does not cause problem in my case but the inconsistency on how 
> memory is used by xen and dom0 can potentially be a problem.

I don't think that matters.  Xen can choose not to use non-2M aligned
pieces of memory if it wants, but that doesn't really affect the dom0
kernel's use of the host E820, because dom0 is only looking for possible
device memory, rather than RAM.

    J
> Allen
>
> -----Original Message-----
> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx] 
> Sent: Friday, January 28, 2011 7:48 AM
> To: Kay, Allen M
> Cc: xen-devel; Stefano Stabellini
> Subject: Re: [Xen-devel] 2.6.32.27 dom0 + latest xen staging boot failure
>
> On Fri, Jan 28, 2011 at 10:28:43AM -0500, Konrad Rzeszutek Wilk wrote:
>> On Thu, Jan 27, 2011 at 10:51:42AM -0800, Kay, Allen M wrote:
>>> Following are the brief error messages from the serial console log.  I have 
>>> also attached the full serial console log and dom0 system map.
>>>
>>> (XEN) mm.c:802:d0 Bad L1 flags 400000
>> On a second look, this is a different issue than I had encountered.
>>
>> The 400000 translates to Xen thinking you had PAGE_GNTTAB set, but that
>> is not right. Googling for this shows that I had fixed this with a
>> Xorg server at some point, but I can't remember the details so that is not
>> that useful :-(
>>
>> You said it works if you give the domain 1024MB, but I wonder if
>> it also works if you disable the IOMMU? What happens then?
> Can you also patch your Xen hypervisor with this patch? It will print out the
> other 89 entries so we can see what type of values they have.. You might need 
> to
> move it a bit as this is for xen-unstable.
>
> diff -r 003acf02d416 xen/arch/x86/mm.c
> --- a/xen/arch/x86/mm.c       Thu Jan 20 17:04:06 2011 +0000
> +++ b/xen/arch/x86/mm.c       Fri Jan 28 10:46:13 2011 -0500
> @@ -1201,11 +1201,12 @@
>      return 0;
>  
>   fail:
> -    MEM_LOG("Failure in alloc_l1_table: entry %d", i);
> +    MEM_LOG("Failure in alloc_l1_table: entry %d of L1 (mfn: %lx). Other L1 
> values:", i, pfn);
>      while ( i-- > 0 )
> -        if ( is_guest_l1_slot(i) )
> +        if ( is_guest_l1_slot(i) ) {
> +            MEM_LOG("L1[%d] = %lx", i, (unsigned 
> long)l1e_get_intpte(pl1e[i]));
>              put_page_from_l1e(pl1e[i], d);
> -
> +     }
>      unmap_domain_page(pl1e);
>      return -EINVAL;
>  }
>
>>> (XEN) mm.c:1204:d0 Failure in alloc_l1_table: entry 90
>>> (XEN) mm.c:2142:d0 Error while validating mfn 1d7e97 (pfn 3d69) for type 
>>> 1000000
>>> 000000000: caf=8000000000000003 taf=1000000000000001
>>> (XEN) mm.c:2965:d0 Error while pinning mfn 1d7e97
>>> (XEN) traps.c:451:d0 Unhandled invalid opcode fault/trap [#6] on VCPU 0 
>>> [ec=0000
>>> ]
>>> (XEN) domain_crash_sync called from entry.S
>>> (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
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