[RFC PATCH 1/3] riscv: Remove 2MB offset in the mm layout

[guoren at kernel.org]

From: Guo Ren <guoren at linux.alibaba.com>

The current RISC-V's mm layout is based on a 2MB offset and wasting
memory. Remove 2MB offset and map PAGE_OFFSET at start_of_DRAM.
Then we could reduce the memory reserved for opensbi in the next
patch.

Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
Cc: Palmer Dabbelt <palmer at dabbelt.com>
Cc: Anup Patel <anup.patel at wdc.com>
Cc: Atish Patra <atishp at rivosinc.com>
---
 arch/riscv/include/asm/page.h   |  8 ++++++++
 arch/riscv/kernel/head.S        | 10 +++-------
 arch/riscv/kernel/vmlinux.lds.S |  5 ++---
 arch/riscv/mm/init.c            | 11 ++++++++---
 4 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
index b3e5ff0125fe..299147c78b4a 100644
--- a/arch/riscv/include/asm/page.h
+++ b/arch/riscv/include/asm/page.h
@@ -16,6 +16,14 @@
 #define PAGE_SIZE	(_AC(1, UL) << PAGE_SHIFT)
 #define PAGE_MASK	(~(PAGE_SIZE - 1))
 
+#if __riscv_xlen == 64
+/* Image load offset(2MB) from start of RAM */
+#define LOAD_OFFSET	0x200000
+#else
+/* Image load offset(4MB) from start of RAM */
+#define LOAD_OFFSET	0x400000
+#endif
+
 #ifdef CONFIG_64BIT
 #define HUGE_MAX_HSTATE		2
 #else
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index f52f01ecbeea..a6ac892d2ccf 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -61,13 +61,7 @@ ENTRY(_start)
 	/* Image load offset (0MB) from start of RAM for M-mode */
 	.dword 0
 #else
-#if __riscv_xlen == 64
-	/* Image load offset(2MB) from start of RAM */
-	.dword 0x200000
-#else
-	/* Image load offset(4MB) from start of RAM */
-	.dword 0x400000
-#endif
+	.dword LOAD_OFFSET
 #endif
 	/* Effective size of kernel image */
 	.dword _end - _start
@@ -94,6 +88,8 @@ relocate:
 	la a1, kernel_map
 	XIP_FIXUP_OFFSET a1
 	REG_L a1, KERNEL_MAP_VIRT_ADDR(a1)
+	li a2, LOAD_OFFSET
+	add a1, a1, a2
 	la a2, _start
 	sub a1, a1, a2
 	add ra, ra, a1
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 5104f3a871e3..75b7c72cd4bd 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -11,10 +11,9 @@
 #else
 
 #include <asm/pgtable.h>
-#define LOAD_OFFSET KERNEL_LINK_ADDR
 
-#include <asm/vmlinux.lds.h>
 #include <asm/page.h>
+#include <asm/vmlinux.lds.h>
 #include <asm/cache.h>
 #include <asm/thread_info.h>
 #include <asm/set_memory.h>
@@ -32,7 +31,7 @@ PECOFF_FILE_ALIGNMENT = 0x200;
 SECTIONS
 {
 	/* Beginning of code and text segment */
-	. = LOAD_OFFSET;
+	. = LOAD_OFFSET + KERNEL_LINK_ADDR;
 	_start = .;
 	HEAD_TEXT_SECTION
 	. = ALIGN(PAGE_SIZE);
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 24b2b8044602..920e78f8c3e4 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -221,6 +221,11 @@ static void __init setup_bootmem(void)
 	if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
 		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
 
+	/*
+	 * Reserve OpenSBI region and depends on PMP to deny accesses.
+	 */
+	memblock_reserve(__pa(PAGE_OFFSET), LOAD_OFFSET);
+
 	early_init_fdt_scan_reserved_mem();
 	dma_contiguous_reserve(dma32_phys_limit);
 	if (IS_ENABLED(CONFIG_64BIT))
@@ -604,7 +609,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 
 	kernel_map.va_kernel_xip_pa_offset = kernel_map.virt_addr - kernel_map.xiprom;
 #else
-	kernel_map.phys_addr = (uintptr_t)(&_start);
+	kernel_map.phys_addr = (uintptr_t)(&_start) - LOAD_OFFSET;
 	kernel_map.size = (uintptr_t)(&_end) - kernel_map.phys_addr;
 #endif
 	kernel_map.va_pa_offset = PAGE_OFFSET - kernel_map.phys_addr;
@@ -645,8 +650,8 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	create_pmd_mapping(trampoline_pmd, kernel_map.virt_addr,
 			   kernel_map.xiprom, PMD_SIZE, PAGE_KERNEL_EXEC);
 #else
-	create_pmd_mapping(trampoline_pmd, kernel_map.virt_addr,
-			   kernel_map.phys_addr, PMD_SIZE, PAGE_KERNEL_EXEC);
+	create_pmd_mapping(trampoline_pmd, kernel_map.virt_addr + LOAD_OFFSET,
+			   kernel_map.phys_addr + LOAD_OFFSET, PMD_SIZE, PAGE_KERNEL_EXEC);
 #endif
 #else
 	/* Setup trampoline PGD */
-- 
2.25.1