grub2/0184-ieee1275-request-memory-with-ibm-client-architecture.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Mon, 6 Feb 2023 10:03:20 -0500
Subject: [PATCH] ieee1275: request memory with ibm,
 client-architecture-support

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>
(cherry picked from commit d5571590b7de61887efac1c298901455697ba307)
---
 grub-core/kern/ieee1275/init.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/grub-core/kern/ieee1275/init.c b/grub-core/kern/ieee1275/init.c
index 8ce1a0f09ee..13e8a5b4bb8 100644
--- a/grub-core/kern/ieee1275/init.c
+++ b/grub-core/kern/ieee1275/init.c
@@ -850,6 +850,19 @@ grub_claim_heap (void)
     }
 #endif
 
+#if defined(__powerpc__)
+  if (grub_ieee1275_test_flag (GRUB_IEEE1275_FLAG_CAN_TRY_CAS_FOR_MORE_MEMORY))
+    {
+      grub_uint64_t rma_size;
+      grub_err_t err;
+
+      err = grub_ieee1275_total_mem (&rma_size);
+      /* if we have an error, don't call CAS, just hope for the best */
+      if (err == GRUB_ERR_NONE && rma_size < (512 * 1024 * 1024))
+	grub_ieee1275_ibm_cas ();
+    }
+#endif
+
   grub_machine_mmap_iterate (heap_init, &total);
 }
 #endif