Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings

From: Sylvain Chouleur
Date: Mon Feb 29 2016 - 05:57:23 EST

2016-02-24 20:45 GMT+01:00 Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>:
> On Wed, 24 Feb, at 10:56:13AM, Linus Torvalds wrote:
>> On Wed, Feb 24, 2016 at 8:36 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> >>
>> >> So the EFI runtime crap should not change once it is mapped. And those
>> >> should be global. It is only natural.
>> >
>> > Why is it natural?
>> >
>> > Long-term, I'd rather see EFI runtime services use an actual mm_struct
>> > and use_mm.
>> Definitely.
>> The EFI runtime page mapping may be unchanging, but that doesn't mean
>> we should be mapping it all the time - the mapping may not change, but
>> we will change away from it.
> There is movement towards hanging the EFI memory map off of mm_struct
> for x86. ARM and arm64 already do this and there were some patches
> from Sylvain (Cc'd) to do this for the purposes of having a task
> context that could be preempted while in the middle of an EFI runtime
> call for some Intel platforms,

I was thinking we could use the efi kthread to handle the efi services
generically, not only for the interruptible case, and have a way to decide if we
allow interruptions inside the efi call itself or not.

Then all runtime services would use an mm_struct. The drawback is that you will
need two context switchs to be able to execute the runtime service.