Joel Savitz [off-list ref] writes:

quoted

On 64-bit powerpc, usage of a non-16MB-aligned value for the mem= kernel
cmdline parameter results in a system hang at boot.

For example, using 'mem=4198400K' will always reproduce this issue.

This patch fixes the problem by aligning any argument to mem= to 16MB
corresponding with the large page size on powerpc.

Fixes: 2babf5c2ec2f ("[PATCH] powerpc: Unify mem= handling")
Co-developed-by: Gonzalo Siero <redacted>
Signed-off-by: Gonzalo Siero <redacted>
Signed-off-by: Joel Savitz <redacted>
---
 arch/powerpc/kernel/prom.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 0b5878c3125b..8cd3e2445d8a 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c

@@ -82,8 +82,12 @@ static int __init early_parse_mem(char *p)
 {
      if (!p)
              return 1;
-
+#ifdef CONFIG_PPC64
+     /* Align to 16 MB == size of ppc64 large page */
+     memory_limit = ALIGN(memparse(p, &p), 0x1000000);
+#else
      memory_limit = PAGE_ALIGN(memparse(p, &p));
+#endif
      DBG("memory limit = 0x%llx\n", memory_limit);

      return 0;
--

2.43.0

Can you try this change?

commit 5555bc55e1aa71f545cff31e1eccdb4a2e39df84
Author: Aneesh Kumar K.V (IBM) [off-list ref]
Date:   Fri Mar 8 14:45:26 2024 +0530

    powerpc/mm: Align memory_limit value specified using mem= kernel parameter

    The value specified for the memory limit is used to set a restriction on
    memory usage. It is important to ensure that this restriction is within
    the linear map kernel address space range. The hash page table
    translation uses a 16MB page size to map the kernel linear map address
    space. htab_bolt_mapping() function aligns down the size of the range
    while mapping kernel linear address space. Since the memblock limit is
    enforced very early during boot, before we can detect the type of memory
    translation (radix vs hash), we align the memory limit value specified
    as a kernel parameter to 16MB. This alignment value will work for both
    hash and radix translations.

    Signed-off-by: Aneesh Kumar K.V (IBM) [off-list ref]

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 0b5878c3125b..9bd965d35352 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c

@@ -824,8 +824,11 @@ void __init early_init_devtree(void *params)
                reserve_crashkernel();
        early_reserve_mem();

-       /* Ensure that total memory size is page-aligned. */
-       limit = ALIGN(memory_limit ?: memblock_phys_mem_size(), PAGE_SIZE);
+       if (memory_limit > memblock_phys_mem_size())
+               memory_limit = 0;
+
+       /* Align down to 16 MB which is large page size with hash page translation */
+       limit = ALIGN_DOWN(memory_limit ?: memblock_phys_mem_size(), SZ_16M);
        memblock_enforce_memory_limit(limit);

 #if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_PPC_4K_PAGES)

diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index e67effdba85c..d6410549e141 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c

@@ -817,8 +817,8 @@ static void __init early_cmdline_parse(void)
                opt += 4;
                prom_memory_limit = prom_memparse(opt, (const char **)&opt);
 #ifdef CONFIG_PPC64
-               /* Align to 16 MB == size of ppc64 large page */
-               prom_memory_limit = ALIGN(prom_memory_limit, 0x1000000);
+               /* Align down to 16 MB which is large page size with hash page translation */
+               prom_memory_limit = ALIGN_DOWN(prom_memory_limit, SZ_16M);
 #endif
        }