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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Aug 29, 2016 at 05:04:05AM -0600, Jan Beulich wrote:
> >>> On 29.08.16 at 01:14, <hakon@xxxxxxxxxxxxxxxxxx> wrote:
> 
> First of all - please don't cross post.
> 
> > 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

It does not look like it was ever applied?

> 
> (this first one that a quick search found)
> 
> > 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)?
> 
> Jan
> 
> 
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