[PATCH] riscv: Start of DRAM should at least be aligned on PMD size for the direct mapping

From: Alexandre Ghiti <alexghiti@rivosinc.com>
To: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Song Shuai <suagrfillet@gmail.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Subject: [PATCH] riscv: Start of DRAM should at least be aligned on PMD size for the direct mapping
Date: Tue,  4 Jul 2023 14:18:37 +0200	[thread overview]
Message-ID: <20230704121837.248976-1-alexghiti@rivosinc.com> (raw)

So that we do not end up mapping the whole linear mapping using 4K
pages, which is slow at boot time, and also very likely at runtime.

So make sure we align the start of DRAM on a PMD boundary.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 arch/riscv/mm/init.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 4fa420faa780..4a43ec275c6d 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -214,8 +214,13 @@ static void __init setup_bootmem(void)
 	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
 
 	phys_ram_end = memblock_end_of_DRAM();
+
+	/*
+	 * Make sure we align the start of the memory on a PMD boundary so that
+	 * at worst, we map the linear mapping with PMD mappings.
+	 */
 	if (!IS_ENABLED(CONFIG_XIP_KERNEL))
-		phys_ram_base = memblock_start_of_DRAM();
+		phys_ram_base = memblock_start_of_DRAM() & PMD_MASK;
 
 	/*
 	 * In 64-bit, any use of __va/__pa before this point is wrong as we
-- 
2.39.2


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