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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.10.2019 14:27, Marek Marczykowski-Górecki  wrote:
> On Wed, Oct 09, 2019 at 02:24:31PM +0200, Jan Beulich wrote:
>> On 09.10.2019 14:21, Marek Marczykowski-Górecki  wrote:
>>> On Wed, Oct 09, 2019 at 02:07:05PM +0200, Jan Beulich wrote:
>>>> On 09.10.2019 13:52, Marek Marczykowski-Górecki  wrote:
>>>>> 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.
>>
>> The concern is about kexec-ing to Linux (based on what I recall
>> from when I wrote this code; as said the situation may have
>> changed for modern Linux).
> 
> But then, Linux won't have EFI system table pointer either, no? I don't
> see Xen passing it over in any way.

Making the system table pointer available e.g. to kexec userspace
(so it can pass it in whatever suitable way) would be an easy
addition. Use of SetVirtualAddressMap(), otoh, would have been a
hard to undo step if I had made Xen's EFI boot path rely on it.
The kexec situation wrt EFI was very much in flux back then, and
hence I didn't want to take unnecessary risks of future
complications. Any step changing the current state of affairs
wants to provide assurance that it doesn't close roads which we
may need to go at some point.

Jan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel