Subject: [PATCH v2 1/2] efi: esrt: use memremap not ioremap to access ESRT table in memory

From: [email-masked] (Matt Fleming)
Date: Tue, 1 Mar 2016 23:30:40 +0000

On Fri, 26 Feb, at 02:41:14PM, Matt Fleming wrote:
> On Thu, 18 Feb, at 02:16:24PM, Peter Jones wrote:
> > 
> > So the question I have is: would you rather chop up regions and reserve
> > the space, or allocate a new copy and update the configuration table
> > (after ExitBootServices()) to point to it?  The latter makes it pretty
> > easy to do from an API that all these drivers can use, and it makes the
> > kexec case completely transparent.
> > 
> > Up to you.
> 
> I think it makes the most sense to chop up the regions we care about
> (i.e. the ones we have drivers for) because not only does that save us
> the effort of copying out the data on every kexec reboot, it also
> prevents us from leaking each copy since we don't free them at the
> moment.
> 
> Then we just need to maintain a separate list of regions to free in
> efi_free_boot_services() or have some other way to distinguish between
> them.
> 
> Oh, and save_runtime_map() would need updating to save Boot Services
> regions too.

I have a very rough draft of patches that implement this strategy on
the 'experiemntal/efi-memmap' branch in the EFI tree if anyone is
curious and wants to take a look. The series will be sent out soon.

I wouldn't necessarily try running them or anything as there's a few
things that I know are broken; ia64 build, EFI mixed mode boot,
probably arm64 regressions.

The upshot of the patch series is that there's a whole lot of code we
can share for manipulating memory maps between all EFI architectures
and by fixing this "reserve boot services regions" in a generic way it
should mean kexec under EFI on arm64 should be fairly trivial to
implement, along with ESRT, etc.