2e645b46e8
On powerpc-ieee1275, we are running out of memory trying to verify
anything. This is because:
- we have to load an entire file into memory to verify it. This is
difficult to change with appended signatures.
- We only have 32MB of heap.
- Distro kernels are now often around 30MB.
So we want to be able to claim more memory from OpenFirmware for our heap
at runtime.
There are some complications:
- The grub mm code isn't the only thing that will make claims on
memory from OpenFirmware:
* PFW/SLOF will have claimed some for their own use.
* The ieee1275 loader will try to find other bits of memory that we
haven't claimed to place the kernel and initrd when we go to boot.
* Once we load Linux, it will also try to claim memory. It claims
memory without any reference to /memory/available, it just starts
at min(top of RMO, 768MB) and works down. So we need to avoid this
area. See arch/powerpc/kernel/prom_init.c as of v5.11.
- The smallest amount of memory a ppc64 KVM guest can have is 256MB.
It doesn't work with distro kernels but can work with custom kernels.
We should maintain support for that. (ppc32 can boot with even less,
and we shouldn't break that either.)
- Even if a VM has more memory, the memory OpenFirmware makes available
as Real Memory Area can be restricted. Even with our CAS work, an LPAR
on a PowerVM box is likely to have only 512MB available to OpenFirmware
even if it has many gigabytes of memory allocated.
What should we do?
We don't know in advance how big the kernel and initrd are going to be,
which makes figuring out how much memory we can take a bit tricky.
To figure out how much memory we should leave unused, I looked at:
- an Ubuntu 20.04.1 ppc64le pseries KVM guest:
vmlinux: ~30MB
initrd: ~50MB
- a RHEL8.2 ppc64le pseries KVM guest:
vmlinux: ~30MB
initrd: ~30MB
So to give us a little wriggle room, I think we want to leave at least
128MB for the loader to put vmlinux and initrd in memory and leave Linux
with space to satisfy its early allocations.
Allow other space to be allocated at runtime.
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
Reviewed-by: Robbie Harwood <rharwood@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is GRUB 2, the second version of the GRand Unified Bootloader. GRUB 2 is rewritten from scratch to make GNU GRUB cleaner, safer, more robust, more powerful, and more portable. See the file NEWS for a description of recent changes to GRUB 2. See the file INSTALL for instructions on how to build and install the GRUB 2 data and program files. See the file MAINTAINERS for information about the GRUB maintainers, etc. If you found a security vulnerability in the GRUB please check the SECURITY file to get more information how to properly report this kind of bugs to the maintainers. Please visit the official web page of GRUB 2, for more information. The URL is <http://www.gnu.org/software/grub/grub.html>. More extensive documentation is available in the Info manual, accessible using 'info grub' after building and installing GRUB 2. There are a number of important user-visible differences from the first version of GRUB, now known as GRUB Legacy. For a summary, please see: info grub Introduction 'Changes from GRUB Legacy'