Re: [PATCH 02/15] [PS3] Get lv1 high memory region from devtree

On 08/03/2011 06:19 PM, Hector Martin wrote:

On 08/04/2011 12:30 AM, Geoff Levand wrote:

quoted

How would a kexec based bootloader work?  If it's kernel were to allocate
high mem and the bootloader program uses the high mem, how could it tell
that kernel not to destroy the region on shutdown?

The current code contemplates the case where a non-kexec based
bootloader is the first stage and allocates highmem (and knows how to
tell the kernel about it), possibly followed by kexec stages that just
keep that allocation. To support a kexec bootloader as the first
bootloader using this mechanism would indeed require extra support to
tell that kernel to retain its allocation, preferably something that can
be decided from userland. Of course the current kexec bootloader
behavior where highmem isn't handed over to the child kernel will still
work.

quoted

If arch/powerpc/boot/ps3.c allocated the mem and added a DT entry
then other OSes that don't know about the Linux device tree won't
be able to use that allocated memory.  Other OSes could do a
test to see if the allocation was already done.  Another option
that might work is to write info into the LV1 repository then
have boot code look there for allocated hig mem.

If you're booting another OS that isn't Linux then it also has no use
for a Linux-specific ramdisk (linux,initrd-start) and thus no use for
preallocated highmem and should be booted as such (maybe make the
userland tools tell the kernel to release highmem if there's no initrd
defined).

This sounds complicated, user programs managing memory regions.

Also, it needs to be considered that a lot of kernels are out
there will be confused if started with high mem already allocated.

Using the lv1 repo is an option, but does it make sense? It's even less
standard than a FDT and we'd have to put both the region1 location and
the initrd location in there (there's no point to maintaining highmem if
you aren't going to use it).

FWIW, the lv1 repo writing hypercalls are unused and undocumented.

The hcalls to create, write, and delete nodes are known, but I don't
recall if I verified they work:

  http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/powerpc/include/asm/lv1call.h;hb=HEAD#l265

#92 should be named lv1_write_repository_node.

You can only modify the repo for your lpar, so:

  lv1_{create,write}_repository_node(n1, n2, n3, n4, v1, v2);
  lv1_delete_repository_node(n1, n2, n3, n4);

-Geoff