[PATCH] arm64: limit MAX_PHYSMEM_BITS based on vmemmap

[D Scott Phillips <scott@os.amperecomputing.com>]

Prior to the memory map adjustments in v6.9-rc1, the amdgpu driver could
trip over the warning of:

`WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END));`

in vmemmap_populate()[1]. After the adjustments, it becomes a translation
fault and panic.

The cause is that the amdgpu driver allocates some unused space from
iomem_resource and claims it as MEMORY_DEVICE_PRIVATE and
devm_memremap_pages() it. An address above those backed by the vmemmap is
used.

Adjust MAX_PHYSMEM_BITS so that addresses not backed by the vmemmap will
not be chosen as device private addresses.

[1]: Call trace:
      vmemmap_populate+0x30/0x48
      __populate_section_memmap+0x40/0x90
      sparse_add_section+0xfc/0x3e8
      __add_pages+0xb4/0x168
      pagemap_range+0x300/0x410
      memremap_pages+0x184/0x2d8
      devm_memremap_pages+0x30/0x90
      kgd2kfd_init_zone_device+0xe0/0x1f0 [amdgpu]
      amdgpu_device_ip_init+0x674/0x888 [amdgpu]
      amdgpu_device_init+0x7bc/0xed8 [amdgpu]
      amdgpu_driver_load_kms+0x28/0x1c0 [amdgpu]
      amdgpu_pci_probe+0x194/0x580 [amdgpu]
      local_pci_probe+0x48/0xb8
      work_for_cpu_fn+0x24/0x40
      process_one_work+0x170/0x3e0
      worker_thread+0x2ac/0x3e0
      kthread+0xf4/0x108
      ret_from_fork+0x10/0x20

Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>
---
 arch/arm64/include/asm/sparsemem.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/sparsemem.h b/arch/arm64/include/asm/sparsemem.h
index 8a8acc220371c..8387301f2e206 100644
--- a/arch/arm64/include/asm/sparsemem.h
+++ b/arch/arm64/include/asm/sparsemem.h
@@ -5,7 +5,7 @@
 #ifndef __ASM_SPARSEMEM_H
 #define __ASM_SPARSEMEM_H
 
-#define MAX_PHYSMEM_BITS	CONFIG_ARM64_PA_BITS
+#define MAX_PHYSMEM_BITS	ilog2(VMEMMAP_RANGE)
 
 /*
  * Section size must be at least 512MB for 64K base
-- 
2.45.2