[PATCH v34 03/14] arm64: limit memory regions based on DT property, usable-memory-range

[AKASHI Takahiro]

Crash dump kernel uses only a limited range of available memory as System
RAM. On arm64 kdump, This memory range is advertised to crash dump kernel
via a device-tree property under /chosen,
   linux,usable-memory-range = <BASE SIZE>

Crash dump kernel reads this property at boot time and calls
memblock_cap_memory_range() to limit usable memory which are listed either
in UEFI memory map table or "memory" nodes of a device tree blob.

Signed-off-by: AKASHI Takahiro <takahiro.aka...@linaro.org>
Reviewed-by: Geoff Levand <ge...@infradead.org>
Acked-by: Catalin Marinas <catalin.mari...@arm.com>
Acked-by: Mark Rutland <mark.rutl...@arm.com>
---
 arch/arm64/mm/init.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index e19e06593e37..290794b1a0f1 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -188,10 +188,45 @@ static int __init early_mem(char *p)
 }
 early_param("mem", early_mem);
 
+static int __init early_init_dt_scan_usablemem(unsigned long node,
+               const char *uname, int depth, void *data)
+{
+       struct memblock_region *usablemem = data;
+       const __be32 *reg;
+       int len;
+
+       if (depth != 1 || strcmp(uname, "chosen") != 0)
+               return 0;
+
+       reg = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
+       if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
+               return 1;
+
+       usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
+       usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
+
+       return 1;
+}
+
+static void __init fdt_enforce_memory_region(void)
+{
+       struct memblock_region reg = {
+               .size = 0,
+       };
+
+       of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
+
+       if (reg.size)
+               memblock_cap_memory_range(reg.base, reg.size);
+}
+
 void __init arm64_memblock_init(void)
 {
        const s64 linear_region_size = -(s64)PAGE_OFFSET;
 
+       /* Handle linux,usable-memory-range property */
+       fdt_enforce_memory_region();
+
        /*
         * Ensure that the linear region takes up exactly half of the kernel
         * virtual address space. This way, we can distinguish a linear address
-- 
2.11.1


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