Re: [Xen-devel] linux-4.7.* under xen-4.6.* gives "unhandled page fault (ec=0000)" at boot. -- Root cause found.

[Håkon Alstadheim <hakon@xxxxxxxxxxxxxxxxxx>]

Den 29. aug. 2016 13:04, skrev Jan Beulich:
>>>> On 29.08.16 at 01:14, <hakon@xxxxxxxxxxxxxxxxxx> wrote:
> Den 17. aug. 2016 21:56, I wrote (to xen-users, as I am no developer):
>>> I'm on gentoo, running gentoo-sources kernel for dom0.
>>>
>>> I am unable to run gentoo-sources-4.7.{0,1}. I'm running under xen,
>>> currently at 4.6.3-r1
>> I am now on linux gentoo-sources-4.7.2, and the bug is stil present.
>>
>> I have done some digging on my own, and found that protecting two instances 
>> of " for_each_efi_memory_desc(md) {" with something like "if( efi.memmap.map 
>> != NULL) {" will allow my dom0 to boot and run.
> Which is basically the equivalent of e.g.
>
> http://lkml.iu.edu/hypermail/linux/kernel/1608.2/03448.html
>
> (this first one that a quick search found)
Thanks :-) . I only googled my problem, not my  half-assed solution.
> My line-numbers may be a bit off due to copious use of pr_info.
>
> The locations are:
> - linux/arch/x86/platform/efi/efi.c line 121 in function efi_find_mirror()
> - /usr/src/linux/arch/x86/platform/efi/quirks.c line 253 in function
> efi_free_boot_services(void)
>
> Searching the web lead me first to a solution which I believe to be
> wrong, changing the comparison operator in for_each_efi_memory_desc. It
> also lead me to someone mentioning that efi.memmap.map is not used when
> running under xen. That info may also be bogus for all I know.
>
> Not sure which part the "bogus" here is meant to apply to: Do you
> mean the statement is bogus (in which case I wonder why), or do
> you mean the data pointed to would be bogus (in which case I
> wonder what data you think about when the pointer is NULL)?
I just mean that I found something on the net and forgot where it came
from, and it should not be taken for truth without independent
verification, i.e. my "solution" might just be nonsense. I'll shut up
now :-) , and go back to lurking.




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