RISC-V: Move DT mapping outof fixmap

Currently, RISC-V reserves 1MB of fixmap memory for device tree. However, it maps only single PMD (2MB) space for fixmap which leaves only < 1MB space left for other kernel features such as early ioremap which requires fixmap as well. The fixmap size can be increased by another 2MB but it brings additional complexity and changes the virtual memory layout as well. If we require some additional feature requiring fixmap again, it has to be moved again. Technically, DT doesn't need a fixmap as the memory occupied by the DT is only used during boot. That's why, We map device tree in early page table using two consecutive PGD mappings at lower addresses (< PAGE_OFFSET). This frees lot of space in fixmap and also makes maximum supported device tree size supported as PGDIR_SIZE. Thus, init memory section can be used for the same purpose as well. This simplifies fixmap implementation. Signed-off-by: Anup Patel <anup.patel@wdc.com> Signed-off-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
mariux64 · Oct 2, 2020 · 8f3a2b4 · 8f3a2b4
1 parent 8a3f30c
commit 8f3a2b4
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Showing 6 changed files with 20 additions and 22 deletions.
diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
@@ -22,9 +22,6 @@
  */
 enum fixed_addresses {
 	FIX_HOLE,
-#define FIX_FDT_SIZE	SZ_1M
-	FIX_FDT_END,
-	FIX_FDT = FIX_FDT_END + FIX_FDT_SIZE / PAGE_SIZE - 1,
 	FIX_PTE,
 	FIX_PMD,
 	FIX_TEXT_POKE1,

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
@@ -464,6 +464,7 @@ static inline void __kernel_map_pages(struct page *page, int numpages, int enabl
 #define kern_addr_valid(addr)   (1) /* FIXME */
 
 extern void *dtb_early_va;
+extern uintptr_t dtb_early_pa;
 void setup_bootmem(void);
 void paging_init(void);
 

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
@@ -258,7 +258,6 @@ clear_bss_done:
 #endif
 	/* Start the kernel */
 	call soc_early_init
-	call parse_dtb
 	tail start_kernel
 
 .Lsecondary_start:

diff --git a/arch/riscv/kernel/head.h b/arch/riscv/kernel/head.h
@@ -16,6 +16,4 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa);
 extern void *__cpu_up_stack_pointer[];
 extern void *__cpu_up_task_pointer[];
 
-void __init parse_dtb(void);
-
 #endif /* __ASM_HEAD_H */
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
@@ -48,8 +48,9 @@ atomic_t hart_lottery __section(.sdata);
 unsigned long boot_cpu_hartid;
 static DEFINE_PER_CPU(struct cpu, cpu_devices);
 
-void __init parse_dtb(void)
+static void __init parse_dtb(void)
 {
+	/* Early scan of device tree from init memory */
 	if (early_init_dt_scan(dtb_early_va))
 		return;
 
@@ -62,6 +63,7 @@ void __init parse_dtb(void)
 
 void __init setup_arch(char **cmdline_p)
 {
+	parse_dtb();
 	init_mm.start_code = (unsigned long) _stext;
 	init_mm.end_code   = (unsigned long) _etext;
 	init_mm.end_data   = (unsigned long) _edata;
@@ -76,7 +78,10 @@ void __init setup_arch(char **cmdline_p)
 #if IS_ENABLED(CONFIG_BUILTIN_DTB)
 	unflatten_and_copy_device_tree();
 #else
-	unflatten_device_tree();
+	if (early_init_dt_verify(__va(dtb_early_pa)))
+		unflatten_device_tree();
+	else
+		pr_err("No DTB found in kernel mappings\n");
 #endif
 
 #ifdef CONFIG_SWIOTLB

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
@@ -28,7 +28,9 @@ unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
 EXPORT_SYMBOL(empty_zero_page);
 
 extern char _start[];
-void *dtb_early_va;
+#define DTB_EARLY_BASE_VA      PGDIR_SIZE
+void *dtb_early_va __initdata;
+uintptr_t dtb_early_pa __initdata;
 
 static void __init zone_sizes_init(void)
 {
@@ -141,8 +143,6 @@ static void __init setup_initrd(void)
 }
 #endif /* CONFIG_BLK_DEV_INITRD */
 
-static phys_addr_t dtb_early_pa __initdata;
-
 void __init setup_bootmem(void)
 {
 	struct memblock_region *reg;
@@ -399,7 +399,7 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
 
 asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 {
-	uintptr_t va, end_va;
+	uintptr_t va, pa, end_va;
 	uintptr_t load_pa = (uintptr_t)(&_start);
 	uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
 	uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
@@ -448,16 +448,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 				   load_pa + (va - PAGE_OFFSET),
 				   map_size, PAGE_KERNEL_EXEC);
 
-	/* Create fixed mapping for early FDT parsing */
-	end_va = __fix_to_virt(FIX_FDT) + FIX_FDT_SIZE;
-	for (va = __fix_to_virt(FIX_FDT); va < end_va; va += PAGE_SIZE)
-		create_pte_mapping(fixmap_pte, va,
-				   dtb_pa + (va - __fix_to_virt(FIX_FDT)),
-				   PAGE_SIZE, PAGE_KERNEL);
-
-	/* Save pointer to DTB for early FDT parsing */
-	dtb_early_va = (void *)fix_to_virt(FIX_FDT) + (dtb_pa & ~PAGE_MASK);
-	/* Save physical address for memblock reservation */
+	/* Create two consecutive PGD mappings for FDT early scan */
+	pa = dtb_pa & ~(PGDIR_SIZE - 1);
+	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA,
+			   pa, PGDIR_SIZE, PAGE_KERNEL);
+	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA + PGDIR_SIZE,
+			   pa + PGDIR_SIZE, PGDIR_SIZE, PAGE_KERNEL);
+	dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PGDIR_SIZE - 1));
 	dtb_early_pa = dtb_pa;
 }
 
@@ -516,6 +513,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 #else
 	dtb_early_va = (void *)dtb_pa;
 #endif
+	dtb_early_pa = dtb_pa;
 }
 
 static inline void setup_vm_final(void)