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On PowerVM, the first time we boot a Linux partition, we may only get 256MB of real memory area, even if the partition has more memory. This isn't enough to reliably verify a kernel. Fortunately, the Power Architecture Platform Reference (PAPR) defines a method we can call to ask for more memory: the broad and powerful ibm,client-architecture-support (CAS) method. CAS can do an enormous amount of things on a PAPR platform: as well as asking for memory, you can set the supported processor level, the interrupt controller, hash vs radix mmu, and so on. If: - we are running under what we think is PowerVM (compatible property of / begins with "IBM"), and - the full amount of RMA is less than 512MB (as determined by the reg property of /memory) then call CAS as follows: (refer to the Linux on Power Architecture Reference, LoPAR, which is public, at B.5.2.3): - Use the "any" PVR value and supply 2 option vectors. - Set option vector 1 (PowerPC Server Processor Architecture Level) to "ignore". - Set option vector 2 with default or Linux-like options, including a min-rma-size of 512MB. - Set option vector 3 to request Floating Point, VMX and Decimal Floating point, but don't abort the boot if we can't get them. - Set option vector 4 to request a minimum VP percentage to 1%, which is what Linux requests, and is below the default of 10%. Without this, some systems with very large or very small configurations fail to boot. This will cause a CAS reboot and the partition will restart with 512MB of RMA. Importantly, grub will notice the 512MB and not call CAS again. Notes about the choices of parameters: - A partition can be configured with only 256MB of memory, which would mean this request couldn't be satisfied, but PFW refuses to load with only 256MB of memory, so it's a bit moot. SLOF will run fine with 256MB, but we will never call CAS under qemu/SLOF because /compatible won't begin with "IBM".) - unspecified CAS vectors take on default values. Some of these values might restrict the ability of certain hardware configurations to boot. This is why we need to specify the VP percentage in vector 4, which is in turn why we need to specify vector 3. Finally, we should have enough memory to verify a kernel, and we will reach Linux. One of the first things Linux does while still running under OpenFirmware is to call CAS with a much fuller set of options (including asking for 512MB of memory). Linux includes a much more restrictive set of PVR values and processor support levels, and this CAS invocation will likely induce another reboot. On this reboot grub will again notice the higher RMA, and not call CAS. We will get to Linux again, Linux will call CAS again, but because the values are now set for Linux this will not induce another CAS reboot and we will finally boot all the way to userspace. On all subsequent boots, everything will be configured with 512MB of RMA, so there will be no further CAS reboots from grub. (phyp is super sticky with the RMA size - it persists even on cold boots. So if you've ever booted Linux in a partition, you'll probably never have grub call CAS. It'll only ever fire the first time a partition loads grub, or if you deliberately lower the amount of memory your partition has below 512MB.) Signed-off-by: Daniel Axtens <dja@axtens.net> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com> Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com> Reviewed-by: Robbie Harwood <rharwood@redhat.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'