linux-kernel - [PATCH] LoongArch: Fix memsection size

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Message-Id: <20221026075638.9396-1-lvjianmin@loongson.cn>
Date:   Wed, 26 Oct 2022 15:56:38 +0800
From:   Jianmin Lv <lvjianmin@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>
Cc:     linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev
Subject: [PATCH] LoongArch: Fix memsection size

On LoongArch, the physical address space ranging from 0 to 0xfffffff is
always memory, which is in the low half of the memsection range from 0 to
0x1fffffff with 512M memsection size, and the high half will be a hole with
invalid memory pages.

This situation may cause some issues. For example, the range of 0x10000000
to 0x1fffffff is io registers, which will be considered as valid memory range
since which is in the memsection of range of 0 to 0x1fffffff. During S3
sleep and resume, these io registers will be saved and restored as valid memory
page (pfn_valid() of common version considers that all pages in a memsection
are valid), which will cause exception, especially when restoring during resume.

We can use 256M size for memsection of LoongArch, or use the way as ARM64 to
walk through all memory memblock to check if a mem pfn is valid which maybe
lower performance. For simplicity, this patch just use the former way.

Signed-off-by: Jianmin Lv <lvjianmin@...ngson.cn>

diff --git a/arch/loongarch/include/asm/sparsemem.h b/arch/loongarch/include/asm/sparsemem.h
index 3d18cdf1b069..05903b40a625 100644
--- a/arch/loongarch/include/asm/sparsemem.h
+++ b/arch/loongarch/include/asm/sparsemem.h
@@ -8,7 +8,7 @@
  * SECTION_SIZE_BITS		2^N: how big each section will be
  * MAX_PHYSMEM_BITS		2^N: how much memory we can have in that space
  */
-#define SECTION_SIZE_BITS	29 /* 2^29 = Largest Huge Page Size */
+#define SECTION_SIZE_BITS	28
 #define MAX_PHYSMEM_BITS	48

 #endif /* CONFIG_SPARSEMEM */
-- 
2.31.1