Re: crash in efi_runtime_call

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 17/04/15 13:39, Jan Beulich wrote:
>>>> On 17.04.15 at 13:59, <andrew.cooper3@citrix.com> 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)

The bug is present in the reference implementation code, which means it
is present in a lot of real firmware.  We have kit from 3 different
vendors which are affected, including latest available firmware.

>
>>> (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

Right or wrong, this is (apparently; I have not checked) what Linux does.

>  - 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).

If I can find some copious free time, I will see about making this happen.

~Andrew