linux-kernel - [PATCH v3] RISC-V: Remove any memblock representing unusable memory area

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Date:   Thu,  1 Oct 2020 12:05:57 -0700
From:   Atish Patra <atish.patra@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Atish Patra <atish.patra@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup.patel@....com>,
        linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Zong Li <zong.li@...ive.com>
Subject: [PATCH v3] RISC-V: Remove any memblock representing unusable memory area

RISC-V limits the physical memory size by -PAGE_OFFSET. Any memory beyond
that size from DRAM start is unusable. Just remove any memblock pointing
to those memory region without worrying about computing the maximum size.

Signed-off-by: Atish Patra <atish.patra@....com>
Reviewed-by: Mike Rapoport <rppt@...ux.ibm.com>

---
Changes from v2->v3
Updated comment as per Mike's suggestion.
---
 arch/riscv/mm/init.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index ca03762a3733..564e0be677b7 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -146,8 +146,6 @@ static phys_addr_t dtb_early_pa __initdata;
 void __init setup_bootmem(void)
 {
 	struct memblock_region *reg;
-	phys_addr_t mem_size = 0;
-	phys_addr_t total_mem = 0;
 	phys_addr_t mem_start, end = 0;
 	phys_addr_t vmlinux_end = __pa_symbol(&_end);
 	phys_addr_t vmlinux_start = __pa_symbol(&_start);
@@ -155,21 +153,18 @@ void __init setup_bootmem(void)
 	/* Find the memory region containing the kernel */
 	for_each_memblock(memory, reg) {
 		end = reg->base + reg->size;
-		if (!total_mem)
+		if (!mem_start)
 			mem_start = reg->base;
 		if (reg->base <= vmlinux_start && vmlinux_end <= end)
 			BUG_ON(reg->size == 0);
-		total_mem = total_mem + reg->size;
 	}
 
 	/*
-	 * Remove memblock from the end of usable area to the
-	 * end of region
+	 * The maximal physical memory size is -PAGE_OFFSET.
+	 * Make sure that any memory beyond mem_start + (-PAGE_OFFSET) is removed
+	 * as it is unusable by kernel.
 	 */
-	mem_size = min(total_mem, (phys_addr_t)-PAGE_OFFSET);
-	if (mem_start + mem_size < end)
-		memblock_remove(mem_start + mem_size,
-				end - mem_start - mem_size);
+	memblock_enforce_memory_limit(mem_start - PAGE_OFFSET);
 
 	/* Reserve from the start of the kernel to the end of the kernel */
 	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
-- 
2.25.1