linux-kernel - [PATCH 2/8] memblock: detect hidden memory hole size

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Date:   Thu, 24 Mar 2022 16:01:52 +0900
From:   Jaewon Kim <jaewon31.kim@...sung.com>
To:     rppt@...nel.org, vbabka@...e.cz, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        ytk.lee@...sung.com, jaewon31.kim@...il.com,
        Jaewon Kim <jaewon31.kim@...sung.com>
Subject: [PATCH 2/8] memblock: detect hidden memory hole size

Bootloader knows the actual memory size, but bootloader may reserve some
memory for a specific purpose and pass the only remaining memory region
to kernel.

Even though kernel does not know what it is, we need to detect those
regions to sum up all reserved memory. Let me call it memory hole. To
expect the hole size, this patch assume two things. One is that each
physical memory has 1GB aligned size and address. And the hole is less
than 1GB. For the hole, let it be shown as unknown in memsize logic.

This is an example.
0x0bf000000-0x0c0000000 0x01000000 (   16384 KB ) nomap unusable unknown

Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>
---
 drivers/of/fdt.c         |  2 ++
 include/linux/memblock.h |  2 ++
 mm/memblock.c            | 45 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index ec2f60a78f8f..9721a3d7b7ae 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -1294,6 +1294,8 @@ void __init early_init_dt_scan_nodes(void)
 
 	/* Handle linux,usable-memory-range property */
 	early_init_dt_check_for_usable_mem_range();
+
+	memblock_memsize_detect_hole();
 }
 
 bool __init early_init_dt_scan(void *params)
diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 468b016e179b..201f8723dfd8 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -608,10 +608,12 @@ static inline void early_memtest(phys_addr_t start, phys_addr_t end)
 extern void memblock_memsize_record(const char *name, phys_addr_t base,
 				    phys_addr_t size, bool nomap,
 				    bool reusable);
+extern void memblock_memsize_detect_hole(void);
 #else
 static inline void memblock_memsize_record(const char *name, phys_addr_t base,
 				    phys_addr_t size, bool nomap,
 				    bool reusable) { }
+static inline void memblock_memsize_detect_hole(void) { }
 #endif
 
 #endif /* _LINUX_MEMBLOCK_H */
diff --git a/mm/memblock.c b/mm/memblock.c
index 8492757f7192..8e032f44eb57 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1970,6 +1970,51 @@ void __init_memblock memblock_memsize_record(const char *name, phys_addr_t base,
 	memblock_dbg("%s %pa..%pa nomap:%d reusable:%d\n",
 		     __func__, &base, &end, nomap, reusable);
 }
+
+/* This function will be called to by early_init_dt_scan_nodes */
+void __init memblock_memsize_detect_hole(void)
+{
+	phys_addr_t base, end;
+	phys_addr_t prev_end, hole_sz;
+	int idx;
+	struct memblock_region *rgn;
+	int memblock_cnt = (int)memblock.memory.cnt;
+
+	/* assume that the hole size is less than 1 GB */
+	for_each_memblock_type(idx, (&memblock.memory), rgn) {
+		prev_end = (idx == 0) ? round_down(rgn->base, SZ_1G) : end;
+		base = rgn->base;
+		end = rgn->base + rgn->size;
+
+		/* only for the last region, check a hole after the region */
+		if (idx + 1 == memblock_cnt) {
+			hole_sz = round_up(end, SZ_1G) - end;
+			if (hole_sz)
+				memblock_memsize_record(NULL, end, hole_sz,
+							true, false);
+		}
+
+		/* for each region, check a hole prior to the region */
+		hole_sz = base - prev_end;
+		if (!hole_sz)
+			continue;
+		if (hole_sz < SZ_1G) {
+			memblock_memsize_record(NULL, prev_end, hole_sz, true,
+						false);
+		} else {
+			phys_addr_t hole_sz1, hole_sz2;
+
+			hole_sz1 = round_up(prev_end, SZ_1G) - prev_end;
+			if (hole_sz1)
+				memblock_memsize_record(NULL, prev_end,
+							hole_sz1, true, false);
+			hole_sz2 = base % SZ_1G;
+			if (hole_sz2)
+				memblock_memsize_record(NULL, base - hole_sz2,
+							hole_sz2, true, false);
+		}
+	}
+}
 #endif /* MEMBLOCK_MEMSIZE */
 
 static void __init free_memmap(unsigned long start_pfn, unsigned long end_pfn)
-- 
2.17.1