Re: [Xen-devel] Xen 4.12 panic on Thinkpad W540 with UEFI mutiboot2, efi=no-rs workarounds it

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.08.2019 18:04, Marek Marczykowski-Górecki  wrote:
> On Wed, Aug 07, 2019 at 05:58:59PM +0200, Jan Beulich wrote:
> > On 07.08.2019 17:51, Marek Marczykowski-Górecki  wrote:
> > > On Wed, Aug 07, 2019 at 05:33:05PM +0200, Jan Beulich wrote:
> > > > On 07.08.2019 17:17, Marek Marczykowski-Górecki  wrote:
> > > > > Actually, I've already tried, but every other build I try, I get even
> > > > > less useful call trace, for example debug unstable build:
> > > > >
> > > > >        Xen call trace:
> > > > >           [<000000007b751c09>] 000000007b751c09
> > > > >           [<8c2b0398e0000daa>] 8c2b0398e0000daa
> > > > > ...
> > > > >        GENERAL PROTECTION FAULT
> > > > >        [error_code=0000]
> > > > But this makes reasonable sense: The faulting insn is "call *0x18(%rax)"
> > > > and %rax is 6954b2b0, which points into a block of type
> > > > EfiBootServicesData (and hence likely reused by the time of the crash
> > > > for other purposes). Hence the "/mapbs" option of xen.efi might help
> > > > here too, but iirc there's no equivalent for it in the MB2 case.
> > > Oh, yes, indeed in Qubes we have /mapbs enabled by default with xen.efi.
> > > I'd like to add it to MB2 case too. Is command line parsed at this point
> > > (efi_exit_boot()) already?
> > I'm struggling a little how to reply, considering that I've already
> > said "iirc there's no equivalent for it in the MB2 case". So I guess
> > I'm simply not understanding your question, or more specifically
> > where you want to get with it.
> /mapbs option is very specific to xen.efi. I'd like to add a means to
> set map_bs variable in MB2 case too. I'm asking whether I can use
> standard command line parser, or do I need something special extracting
> it from MB2 structures directly.
Well, efi_multiboot2() gets called from head.S, even before the
(non-EFI only) cmdline_parse_early. I don't suppose there's a way
to avoid mixing this new option into the "normal" command line,
and hence there's also no way around peeking into the command
line early. Of course there's the option to see whether what
efi_arch_process_memory_map() could be deferred until later. But
likely that would be a far more intrusive change than what you're
considering to carry out.

Jan

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