linux-kernel - [PATCH] RISC-V: Fix Maximum Physical Memory 2GiB option for 64bit systems

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Date:   Tue, 2 Apr 2019 06:02:38 +0000
From:   Anup Patel <Anup.Patel@....com>
To:     Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>
CC:     Atish Patra <Atish.Patra@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Anup Patel <Anup.Patel@....com>
Subject: [PATCH] RISC-V: Fix Maximum Physical Memory 2GiB option for 64bit
 systems

The Maximum Physical Memory 2GiB option for 64bit systems is currently
broken because kernel hangs at boot-time when this option is enabled
and the underlying system has more than 2GiB memory.

This issue can be easily reproduced on SiFive Unleashed board where
we have 8GiB of memory.

This patch fixes above issue by reserving unusable memory region in
setup_bootmem().

Signed-off-by: Anup Patel <anup.patel@....com>
---
 arch/riscv/mm/init.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 5fd8c922e1c2..6b063f20a9d0 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -121,6 +121,14 @@ void __init setup_bootmem(void)
 			 */
 			memblock_reserve(reg->base, vmlinux_end - reg->base);
 			mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
+
+			/*
+			 * Reserve from the end of usable area to the end of
+			 * region
+			 */
+			if ((reg->base + mem_size) < end)
+				memblock_reserve(reg->base + mem_size,
+						 end - reg->base - mem_size);
 		}
 	}
 	BUG_ON(mem_size == 0);
-- 
2.17.1