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

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Wed, Oct 09, 2019 at 02:07:05PM +0200, Jan Beulich wrote:
> On 09.10.2019 13:52, Marek Marczykowski-Górecki  wrote:
> > On Wed, Oct 09, 2019 at 01:48:38PM +0200, Jan Beulich wrote:
> >> On 09.10.2019 13:00, Marek Marczykowski-Górecki  wrote:
> >>> On Wed, Oct 09, 2019 at 12:50:09PM +0200, Jan Beulich wrote:
> >>>> On 09.10.2019 12:31, Marek Marczykowski-Górecki  wrote:
> >>>>> BTW How runtime services work after kexec? I don't see EFI handles
> >>>>> handed over kexec, are they somehow re-discovered?
> >>>>
> >>>> What EFI handles are you talking about? For runtime services
> >>>> what a consumer needs is a table pointer, which is a field
> >>>> in the system table, which in turn is an argument passed to
> >>>> the EFI application's entry point.
> >>>
> >>> Yes, I'm talking about those pointers (system table specifically).
> >>>
> >>>> I didn't think there are
> >>>> provisions in the spec for either of these pointers being NULL.
> >>>
> >>> But I don't see kexec using EFI application entry point. Am I missing
> >>> something?
> >>
> >> Can we stop thinking about a Linux -> Xen transition on this
> >> thread please? 
> > 
> > I'm talking about Xen->Xen transition here. How system table pointer is
> > passed from old Xen to new Xen instance? And how the new Xen instance
> > deals with boot services being not available anymore?
> 
> It doesn't. I should better have said "* -> Xen transitions" in
> my earlier reply. I simply can't see how this can all work with
> EFI underneath without some extra conveying of data from the old
> to the new instance.

Does it mean the whole discussion about SetVirtualAddressMap() being
incompatible with kexec is moot, because runtime services (including
SetVirtualAddressMap()) are not used by Xen after kexec anyway? If I
understand correctly, you just said the Xen after kexec don't have
runtime services pointer.
If not, can you explain what exactly is the case when second call to
SetVirtualAddressMap() could happen (being the reason for #ifdef-ing it
out in efi/boot.c)?

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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