On Wed, Feb 24, 2016 at 11:45 AM, Matt Fleming <[email protected]> wrote: > On Wed, 24 Feb, at 10:56:13AM, Linus Torvalds wrote: >> On Wed, Feb 24, 2016 at 8:36 AM, Andy Lutomirski <[email protected]> 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, > > > https://lkml.kernel.org/r/[email protected] > > Apart from the code simplification and not being required to open-code > the %cr3 diddling, are there other benefits of mm_struct and use_mm() > that make it appealing in the non-preemptible case? > > Not that those aren't reasons enough.
If we add PCID support, then use_mm will get the benefits (~200ns savings for a round trip) for free. > >> So marking those pages global is very wrong. > > Ingo, Andy, how do you want to handle this patch? Maybe just drop it > from tip/efi/core while we prod around making all the EFI mappings > non-global? Nothing else depends on it, it can be dropped without any > harm. If the patch is harmless as is, I'm okay with letting it stay. --Andy -- Andy Lutomirski AMA Capital Management, LLC
