[PATCH v5 2/4] MIPS: Refactor early_parse_mem() to fix mem= parameter

[Tiezhu Yang]

According to Documentation/admin-guide/kernel-parameters.txt,
the kernel command-line parameter mem= means "Force usage of
a specific amount of memory", but when add "mem=3G" to the
command-line, kernel boot hangs in sparse_init(), the same
issue appears when add "mem=3G@64M".

Here are the logs with "mem=3G@64M memblock=debug" added to
the kernel command line before the hang:

  [    0.000000] Linux version 5.17.0-rc3+ (loongson@linux)
  [    0.000000] CpuClock = 1800000000
  [    0.000000] The bridge chip is LS7A
  [    0.000000] CP0_Config3: CP0 16.3 (0xdc8030a0)
  [    0.000000] CP0_PageGrain: CP0 5.1 (0x28000000)
  [    0.000000] NUMA: Discovered 4 cpus on 1 nodes
  [    0.000000] Node0: mem_type:1, mem_start:0x200000, mem_size:0xee MB
  [    0.000000]        start_pfn:0x80, end_pfn:0x3c00, num_physpages:0x3b80
  [    0.000000] Node0: mem_type:2, mem_start:0x90200000, mem_size:0x6fe MB
  [    0.000000]        start_pfn:0x24080, end_pfn:0x40000, num_physpages:0x1fb00
  [    0.000000] Node0: mem_type:2, mem_start:0x120000000, mem_size:0x1600 MB
  [    0.000000]        start_pfn:0x48000, end_pfn:0xa0000, num_physpages:0x77b00
  [    0.000000] Node0's addrspace_offset is 0x0
  [    0.000000] Node0: start_pfn=0x80, end_pfn=0xa0000
  [    0.000000] NUMA: set cpumask cpu 0 on node 0
  [    0.000000] NUMA: set cpumask cpu 1 on node 0
  [    0.000000] NUMA: set cpumask cpu 2 on node 0
  [    0.000000] NUMA: set cpumask cpu 3 on node 0
  [    0.000000] printk: bootconsole [early0] enabled
  [    0.000000] CPU0 revision is: 0014c001 (ICT Loongson-3)
  [    0.000000] FPU revision is: 00f70501
  [    0.000000] MSA revision is: 00060140
  [    0.000000] OF: fdt: No chosen node found, continuing without
  [    0.000000] MIPS: machine is loongson,loongson64g-4core-ls7a
  [    0.000000] User-defined physical RAM map overwrite
  [    0.000000] Kernel sections are not in the memory maps
  [    0.000000] memblock_add: [0x0000000000200000-0x000000000231185f] setup_arch+0x140/0x794
  [    0.000000] memblock_reserve: [0x0000000001260520-0x0000000001262560] setup_arch+0x148/0x794
  [    0.000000] Initrd not found or empty - disabling initrd
  [    0.000000] memblock_alloc_try_nid: 8257 bytes align=0x40 nid=-1 from=0x0000000000000000 max_addr=0x0000000000000000 early_init_dt_alloc_memory_arch+0x30/0x60
  [    0.000000] memblock_reserve: [0x0000000004000000-0x0000000004002040] memblock_alloc_range_nid+0xf0/0x178
  [    0.000000] memblock_alloc_try_nid: 37972 bytes align=0x8 nid=-1 from=0x0000000000000000 max_addr=0x0000000000000000 early_init_dt_alloc_memory_arch+0x30/0x60
  [    0.000000] memblock_reserve: [0x0000000004002048-0x000000000400b49b] memblock_alloc_range_nid+0xf0/0x178

As Mike Rapoport said, the kernel lives in 0x200000 and using
mem=3G@64M removes the memory with the kernel and also makes
the kernel think there is memory between 0x400000 and 0xf000000
while there seem to be a hole up to 0x90200000. This definitely
can be reason for the hangs.

This commit is similar with the implementation of the other
archs such as arm64, powerpc and riscv, refactor the function
early_parse_mem() and then use memblock_mem_range_remove_map()
to support mem=limit and mem=limit@base (if @base is omitted,
it is equivalent to mem=limit).

With this patch, when add "mem=3G" to the command-line, the kernel boots
successfully, we can see the following messages:

  [    0.000000] Memory limited to 0MB-3072MB
  ...
  [    0.000000] Early memory node ranges
  [    0.000000]   node   0: [mem 0x0000000000200000-0x000000000effffff]
  [    0.000000]   node   0: [mem 0x0000000090200000-0x00000000ffffffff]
  [    0.000000]   node   0: [mem 0x0000000120000000-0x00000001613fffff]
  ...
  [    0.000000] Memory: 3005280K/3145728K available (...)

When add "mem=3G@64M" to the command-line, the kernel boots successfully,
we can see the following messages:

  [    0.000000] Memory limited to 64MB-3136MB
  ...
  [    0.000000] Early memory node ranges
  [    0.000000]   node   0: [mem 0x0000000004000000-0x000000000effffff]
  [    0.000000]   node   0: [mem 0x0000000090200000-0x00000000ffffffff]
  [    0.000000]   node   0: [mem 0x0000000120000000-0x00000001653fffff]
  ...
  [    0.000000] Memory: 3070816K/3147776K available (...)

After login, the output of free command is consistent with the
above log.

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---
 arch/mips/kernel/setup.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index f979adf..de5824bc 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -339,27 +339,20 @@ static void __init bootmem_init(void)
 #endif	/* CONFIG_SGI_IP27 */
 
 static int usermem __initdata;
+static phys_addr_t memory_limit;
+static phys_addr_t memory_base;
 
 static int __init early_parse_mem(char *p)
 {
-	phys_addr_t start, size;
+	if (!p)
+		return 1;
 
-	/*
-	 * If a user specifies memory size, we
-	 * blow away any automatically generated
-	 * size.
-	 */
-	if (usermem == 0) {
-		usermem = 1;
-		memblock_remove(memblock_start_of_DRAM(),
-			memblock_end_of_DRAM() - memblock_start_of_DRAM());
-	}
-	start = 0;
-	size = memparse(p, &p);
+	memory_limit = memparse(p, &p) & PAGE_MASK;
 	if (*p == '@')
-		start = memparse(p + 1, &p);
+		memory_base = memparse(p + 1, &p) & PAGE_MASK;
 
-	memblock_add(start, size);
+	pr_notice("Memory limited to %lluMB-%lluMB\n",
+		  (u64)memory_base >> 20, (u64)(memory_base + memory_limit) >> 20);
 
 	return 0;
 }
@@ -678,6 +671,10 @@ static void __init arch_mem_init(char **cmdline_p)
 	memblock_reserve(__pa_symbol(&__nosave_begin),
 		__pa_symbol(&__nosave_end) - __pa_symbol(&__nosave_begin));
 
+	/* Limit the memory. */
+	memblock_mem_range_remove_map(memory_base, memory_limit);
+	memblock_allow_resize();
+
 	early_memtest(PFN_PHYS(ARCH_PFN_OFFSET), PFN_PHYS(max_low_pfn));
 }
 
-- 
2.1.0