powerpc: increase MIN RMA size for CAS negotiation

Change RMA size from 512 MB to 768 MB which will result
in more memory at boot time for PowerPC. When vTPM, Secure Boot or
FADump are enabled on PowerPC, the 512 MB RMA memory is not sufficient for
booting. With this 512 MB RMA, GRUB2 runs out of memory and fails to
boot the machine. Sometimes even usage of CDROM requires more memory
for installation and along with the options mentioned above exhausts
the boot memory which results in boot failures. Increasing the RMA size
will resolves multiple out of memory issues observed in PowerPC.

Failure details (GRUB2 debugs):

  kern/ieee1275/init.c:550: mm requested region of size 8513000, flags 1
  kern/ieee1275/init.c:563: Cannot satisfy allocation and retain minimum runtime space
  kern/ieee1275/init.c:550: mm requested region of size 8513000, flags 0
  kern/ieee1275/init.c:563: Cannot satisfy allocation and retain minimum runtime space
  kern/file.c:215: Closing `/ppc/ppc64/initrd.img' ...
  kern/disk.c:297: Closing `ieee1275//vdevice/v-scsi@30000067/disk@8300000000000000'...
  kern/disk.c:311: Closing `ieee1275//vdevice/v-scsi@30000067/disk@8300000000000000' succeeded.
  kern/file.c:225: Closing `/ppc/ppc64/initrd.img' failed with 3.
  kern/file.c:148: Opening `/ppc/ppc64/initrd.img' succeeded.
  error: ../../grub-core/kern/mm.c:552:out of memory.

Signed-off-by: Avnish Chouhan <[email protected]>

Author: Avnish Chouhan

grub-core/kern/ieee1275/init.c

@@ -737,7 +737,7 @@ struct cas_vector
 
 /*
  * Call ibm,client-architecture-support to try to get more RMA.
- * We ask for 512MB which should be enough to verify a distro kernel.
+ * We ask for 768MB which should be enough to verify a distro kernel.
  * We ignore most errors: if we don't succeed we'll proceed with whatever
  * memory we have.
  */
@@ -809,7 +809,7 @@ grub_ieee1275_ibm_cas (void)
     .vec1 = 0x80, /* ignore */
     .vec2_size = 1 + sizeof (struct option_vector2) - 2,
     .vec2 = {
-      0, 0, -1, -1, -1, -1, -1, 512, -1, 0, 48
+      0, 0, -1, -1, -1, -1, -1, 768, -1, 0, 48
     },
     .vec3_size = 2 - 1,
     .vec3 = 0x00e0, /* ask for FP + VMX + DFP but don't halt if unsatisfied */
@@ -846,6 +846,10 @@ grub_claim_heap (void)
 {
   grub_err_t err;
   grub_uint32_t total = HEAP_MAX_SIZE;
+#if defined(__powerpc__)
+  grub_uint32_t ibm_ca_support_reboot = 0;
+  grub_ssize_t actual;
+#endif
 
   err = grub_ieee1275_total_mem (&rmo_top);
 
@@ -858,11 +862,48 @@ grub_claim_heap (void)
     grub_mm_add_region_fn = grub_ieee1275_mm_add_region;
 
 #if defined(__powerpc__)
+  /* Check if it's a CAS reboot with below property. If so, we will skip CAS call */
+  if (grub_ieee1275_get_integer_property (grub_ieee1275_chosen,
+                                          "ibm,client-architecture-support-reboot",
+                                          &ibm_ca_support_reboot,
+                                          sizeof (ibm_ca_support_reboot),
+                                          &actual) >= 0)
+    grub_dprintf ("ieee1275", "ibm,client-architecture-support-reboot: %" PRIuGRUB_UINT32_T "\n",
+                  ibm_ca_support_reboot);
+
   if (grub_ieee1275_test_flag (GRUB_IEEE1275_FLAG_CAN_TRY_CAS_FOR_MORE_MEMORY))
     {
-      /* if we have an error, don't call CAS, just hope for the best */
-      if (err == GRUB_ERR_NONE && rmo_top < (512 * 1024 * 1024))
-	grub_ieee1275_ibm_cas ();
+      /*
+       * If we have an error, don't call CAS. Just hope for the best.
+       * Along with the above, if the rmo_top is 512 MB or above. We
+       * will skip the CAS call. However, if we call CAS, the rmo_top
+       * will be set to 768 MB via CAS Vector2. But we need to call
+       * CAS with "rmo_top < 512 MB" to avoid the issue on the older
+       * Linux kernel, which still uses rmo_top as 512 MB. If we call
+       * CAS with a condition "rmo_top < 768 MB", it will result in an
+       * issue due to the IBM CAS reboot feature and we won't be able
+       * to boot the newer kernel. Whenever a reboot is detected as
+       * the CAS reboot by GRUB. It will boot the machine with the
+       * last booted kernel by reading the variable "boot-last-label"
+       * which has the info related to the last boot and it's specific
+       * to IBM PowerPC. Due to this, the machine will boot with the
+       * last booted kernel which has rmo_top as 512 MB. Also, if the
+       * reboot is detected as a CAS reboot, the GRUB will skip the CAS
+       * call. As the CAS has already been called earlier, so it is
+       * not required to call CAS even if the other conditions are met.
+       * This condition will also prevent a scenario where the machine
+       * get stuck in the CAS reboot loop while booting. A machine with
+       * an older kernel, having option_vector2 MIN_RMA as 512 MB in
+       * Linux prom_init.c and GRUB uses "rmo_top < 768 MB" condition
+       * for calling CAS. Due to their respective conditions, linux
+       * CAS and GRUB CAS will keep doing the CAS calls and change
+       * the MIN_RMA from 768(changed by GRUB) to 512(changed by Linux)
+       * to 768(changed by GRUB) to 512(changed by Linux) and so on,
+       * and the machine will stuck in this CAS reboot loop forever.
+       * IBM PAPR : https://openpower.foundation/specifications/linuxonpower/
+       */
+      if (!ibm_ca_support_reboot && err == GRUB_ERR_NONE && rmo_top < (512 * 1024 * 1024))
+        grub_ieee1275_ibm_cas ();
     }
 #endif