Re: [Xen-devel] crash in efi_runtime_call

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.04.15 at 13:59, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 17/04/15 12:17, Olaf Hering wrote:
>> Since booting xen fails on my ProBook unless I specify "maxcpus=1" I
>> tried the EFI firmware today. To my surprise it boots and finds all
>> cpus. But once some efi driver in dom0 is loaded xen crashes. The same
>> happens with xen-4.4 as included in SLE12.
>>
>> ...
>> (XEN) Xen call trace:
>> (XEN)    [<00000000aec1e8e1>] 00000000aec1e8e1
>> (XEN)    [<ffff82d080222600>] efi_runtime_call+0x7f0/0x890
>> (XEN)    [<ffff82d0801641a9>] do_platform_op+0x679/0x1670
>> (XEN)    [<ffff82d08021dfb9>] syscall_enter+0xa9/0xae
>> ....
>>
>> Can I do anything about it, or is this a firmware bug? I will move the
>> offending efi driver away and try again.
>>
>> Olaf
> 
> This is a firmware bug.

+1 (and I'm surprised how common this is)

>> (XEN)  0000100000000-000023fffffff type=7 attr=000000000000000
>> (XEN)  00000fec10000-00000fec10fff type=11 attr=8000000000000001
>> (XEN)  00000fff40000-00000fff46fff type=11 attr=8000000000000000
>> (XEN) Unknown cachability for MFNs 0xfff40-0xfff46
> 
> This unknown cacheability causes Xen not to make pagetables for the region.
> 
> There is a patch or two floating around the list, but currently no
> resolution on the argument it created.
> 
> https://github.com/xenserver/xen-4.5.pg/blob/master/master/unknown-cacheabilit
>  
> y.patch
> is the XenServer fix.

Now that's surely wrong - if anything, unknown should be treated as
UC (and quite likely specifically in a case like the one Olaf reports here,
as the offending memory range pretty likely is other than normal RAM).
What I'd accept as a patch would be the addition of a command line
option enforcing the mapping of such unknown cacheability areas with
a certain caching type (default then being UC).

Jan


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