Re: [PATCH v2] Use EfiACPIReclaimMemory for ESRT

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.10.2022 18:52, Demi Marie Obenour wrote:
> On Tue, Oct 11, 2022 at 11:59:01AM +0200, Jan Beulich wrote:
>> On 11.10.2022 05:42, Demi Marie Obenour wrote:
>>> A previous patch tried to get Linux to use the ESRT under Xen if it is
>>> in memory of type EfiRuntimeServicesData.  However, this turns out to be
>>> a bad idea.  Ard Biesheuvel pointed out that EfiRuntimeServices* memory
>>> winds up fragmenting both the EFI page tables and the direct map,
>>
>> Can this statement please be made describe Xen, not Linux? Aiui at least
>> the directmap aspect doesn't apply to Xen.
> 
> Should it apply to Xen?  My understanding is that Ard’s statements
> regarding mismatched attributes refer to any kernel, not just Linux.
> You would be in a better position to judge that, though.

We run EFI runtime services functions on their own page tables (with
certain areas copied from the directmap). With EfiACPIReclaimMemory
converted to E820_ACPI we do not insert those ranges into the directmap
(i.e. no difference to EfiRuntimeServices*). At least this latter fact
means fragmentation effects - if they exist - are the same for both
types.

>>> and
>>> that EfiACPIReclaimMemory is a much better choice for this purpose.
>>
>> I think the "better" wants explaining here, without requiring people to
>> follow ...
> 
> Something like, “EfiACPIReclaimMemory is the correct type for
> configuration tables that are only used by the OS.”?

Preferably with "supposedly" inserted, unless you (or Ard) can point
out a place in the spec where this is actually written down.

Jan