On 06/26/2013 07:38 AM, James Bottomley wrote:

On Wed, 2013-06-26 at 14:59 +0100, Matt Fleming wrote:

quoted

On Wed, 26 Jun, at 03:53:11PM, Leif Lindholm wrote:

quoted

It's completely feasible, but we'd need to use a different method to do
the boot services call with a 1:1 mapping (idmap support is not available
until much later in the boot process).

At least if you no longer relied upon the idmap we could potentially
have a single efi_enter_virtual_mode() call-site in init/main.c, which
would be nice.

The fixed virtual address scheme currently being looked at for x86_64 to
make SetVirtualAddressMap() kexec invariant doesn't work on 32 bit
because the address space isn't big enough.  For ARM, given that we've
much more opportunity to work with the vendors, can we just avoid
transitioning to a virtual address map and always just install a
physical mapping before doing efi calls?

What we could do on x86-32 is to map from 0xc0000000 downwards.  It
wouldn't be invariant across kernel builds with different user/kernel
split... but I'm not sure we can win that one.

The other option is to say sod it and just use straight 1:1 mapping on
32 bits...

	-hpa