Merge: Description: Updates for Grub RMA size

MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-10/-/merge_requests/11

JIRA: https://issues.redhat.com/browse/RHEL-70827

Build Info: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=66721363

Tested: Verified Brew build test kernel RPMs

This issue occurred due to lack of available memory in RMA region (Earlier size 512 MB, New size after the fix : 768 MB) for Grub2.
The below observations and testings are done with just the kernel fixes (No Grub2 fixes are included).

________

Without the fix:

The following errors are observed in Grub2 followed by kernel panic:

*****

error: ../../grub-core/kern/mm.c:552:out of memory.
.
.
[    0.777633] List of all partitions:
[    0.777639] No filesystem could mount root, tried:
[    0.777649] Kernel panic - not syncing: VFS: Unable to mount root fs on "" or unknown-block(0,0)

--And the memory looks like this below:

memory layout at init:
  memory_limit : 0000000000000000 (16 MB aligned)
  alloc_bottom : 00000000108b0000
  alloc_top    : 0000000020000000
  alloc_top_hi : 0000000020000000
  rmo_top      : 0000000020000000  <<<<< RMA
  ram_top      : 0000000020000000

*****
_________

After the fix :

None of the earlier errors were observed while booting. The RMA size has increased to 768 MB and the same can be seen while booting.

*****

memory layout at init:
  memory_limit : 0000000000000000 (16 MB aligned)
  alloc_bottom : 0000000010e20000
  alloc_top    : 0000000030000000
  alloc_top_hi : 0000000040000000
  rmo_top      : 0000000030000000  <<<<<RMA
  ram_top      : 0000000040000000

*****

________

FADump impact:

This increase in RMA size to 768 MB has impacted the FADump. We have fixed this impact in FADump and the patch series has been tested with the following four scenarios, and both the production kernel and FADump kernel boot successfully:

1. Production Kernel: RADIX MMU
   FADump Kernel:     RADIX MMU
   - MIN_RMA: 768 MB
   - RMA:     1 GB
     - a. crashkernel: 4 GB
     - b. crashkernel: 1 GB

2. Production Kernel: HASH MMU
   FADump Kernel:   HASH MMU
   - MIN_RMA: 768 MB
   - RMA:     1 GB
     - a. crashkernel: 768 MB
     - b. crashkernel: 1 GB

________

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Approved-by: Tony Camuso <tcamuso@redhat.com>
Approved-by: Eder Zulian <ezulian@redhat.com>
Approved-by: Steve Best <sbest@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Jan Stancek <jstancek@redhat.com>

Author: jstancek

Documentation/ABI/testing/sysfs-kernel-fadump

@@ -55,4 +55,5 @@ Date:		May 2024
 Contact:	linuxppc-dev@lists.ozlabs.org
 Description:	read/write
 		This is a special sysfs file available to setup additional
-		parameters to be passed to capture kernel.
+		parameters to be passed to capture kernel. For HASH MMU it
+		is exported only if RMA size higher than 768MB.

Documentation/arch/powerpc/firmware-assisted-dump.rst

@@ -120,6 +120,28 @@ to ensure that crash data is preserved to process later.
    e.g.
      # echo 1 > /sys/firmware/opal/mpipl/release_core
 
+-- Support for Additional Kernel Arguments in Fadump
+   Fadump has a feature that allows passing additional kernel arguments
+   to the fadump kernel. This feature was primarily designed to disable
+   kernel functionalities that are not required for the fadump kernel
+   and to reduce its memory footprint while collecting the dump.
+
+  Command to Add Additional Kernel Parameters to Fadump:
+  e.g.
+  # echo "nr_cpus=16" > /sys/kernel/fadump/bootargs_append
+
+  The above command is sufficient to add additional arguments to fadump.
+  An explicit service restart is not required.
+
+  Command to Retrieve the Additional Fadump Arguments:
+  e.g.
+  # cat /sys/kernel/fadump/bootargs_append
+
+Note: Additional kernel arguments for fadump with HASH MMU is only
+      supported if the RMA size is greater than 768 MB. If the RMA
+      size is less than 768 MB, the kernel does not export the
+      /sys/kernel/fadump/bootargs_append sysfs node.
+
 Implementation details:
 -----------------------
 

arch/powerpc/include/asm/prom.h

@@ -17,6 +17,8 @@
 struct device_node;
 struct property;
 
+#define MIN_RMA			768		/* Minimum RMA (in MB) for CAS negotiation */
+
 #define OF_DT_BEGIN_NODE	0x1		/* Start of node, full name */
 #define OF_DT_END_NODE		0x2		/* End node */
 #define OF_DT_PROP		0x3		/* Property: name off, size,

arch/powerpc/kernel/fadump.c

@@ -33,6 +33,7 @@
 #include <asm/fadump-internal.h>
 #include <asm/setup.h>
 #include <asm/interrupt.h>
+#include <asm/prom.h>
 
 /*
  * The CPU who acquired the lock to trigger the fadump crash should
@@ -1763,19 +1764,19 @@ void __init fadump_setup_param_area(void)
 		range_end = memblock_end_of_DRAM();
 	} else {
 		/*
-		 * Passing additional parameters is supported for hash MMU only
-		 * if the first memory block size is 768MB or higher.
+		 * Memory range for passing additional parameters for HASH MMU
+		 * must meet the following conditions:
+		 * 1. The first memory block size must be higher than the
+		 *    minimum RMA (MIN_RMA) size. Bootloader can use memory
+		 *    upto RMA size. So it should be avoided.
+		 * 2. The range should be between MIN_RMA and RMA size (ppc64_rma_size)
+		 * 3. It must not overlap with the fadump reserved area.
 		 */
-		if (ppc64_rma_size < 0x30000000)
+		if (ppc64_rma_size < MIN_RMA*1024*1024)
 			return;
 
-		/*
-		 * 640 MB to 768 MB is not used by PFW/bootloader. So, try reserving
-		 * memory for passing additional parameters in this range to avoid
-		 * being stomped on by PFW/bootloader.
-		 */
-		range_start = 0x2A000000;
-		range_end = range_start + 0x4000000;
+		range_start = MIN_RMA * 1024 * 1024;
+		range_end = min(ppc64_rma_size, fw_dump.boot_mem_top);
 	}
 
 	fw_dump.param_area = memblock_phys_alloc_range(COMMAND_LINE_SIZE,

arch/powerpc/kernel/prom_init.c

@@ -1061,7 +1061,7 @@ static const struct ibm_arch_vec ibm_architecture_vec_template __initconst = {
 		.virt_base = cpu_to_be32(0xffffffff),
 		.virt_size = cpu_to_be32(0xffffffff),
 		.load_base = cpu_to_be32(0xffffffff),
-		.min_rma = cpu_to_be32(512),		/* 512MB min RMA */
+		.min_rma = cpu_to_be32(MIN_RMA),
 		.min_load = cpu_to_be32(0xffffffff),	/* full client load */
 		.min_rma_percent = 0,	/* min RMA percentage of total RAM */
 		.max_pft_size = 48,	/* max log_2(hash table size) */