path: root/arch/riscv/include/asm/pgtable.h
diff options
authorAnup Patel <Anup.Patel@wdc.com>2019-06-28 13:36:21 -0700
committerPaul Walmsley <paul.walmsley@sifive.com>2019-07-09 09:08:04 -0700
commit671f9a3e2e24cdeb2d2856abee7422f093e23e29 (patch)
tree12c0271582f801f9dc2b0a2be59ee891e6c5f99f /arch/riscv/include/asm/pgtable.h
parent2ebca1cbb4a5a31f8d89f22d9d410b432a97f7a7 (diff)
RISC-V: Setup initial page tables in two stages
Currently, the setup_vm() does initial page table setup in one-shot very early before enabling MMU. Due to this, the setup_vm() has to map all possible kernel virtual addresses since it does not know size and location of RAM. This means we have kernel mappings for non-existent RAM and any buggy driver (or kernel) code doing out-of-bound access to RAM will not fault and cause underterministic behaviour. Further, the setup_vm() creates PMD mappings (i.e. 2M mappings) for RV64 systems. This means for PAGE_OFFSET=0xffffffe000000000 (i.e. MAXPHYSMEM_128GB=y), the setup_vm() will require 129 pages (i.e. 516 KB) of memory for initial page tables which is never freed. The memory required for initial page tables will further increase if we chose a lower value of PAGE_OFFSET (e.g. 0xffffff0000000000) This patch implements two-staged initial page table setup, as follows: 1. Early (i.e. setup_vm()): This stage maps kernel image and DTB in a early page table (i.e. early_pg_dir). The early_pg_dir will be used only by boot HART so it can be freed as-part of init memory free-up. 2. Final (i.e. setup_vm_final()): This stage maps all possible RAM banks in the final page table (i.e. swapper_pg_dir). The boot HART will start using swapper_pg_dir at the end of setup_vm_final(). All non-boot HARTs directly use the swapper_pg_dir created by boot HART. We have following advantages with this new approach: 1. Kernel mappings for non-existent RAM don't exists anymore. 2. Memory consumed by initial page tables is now indpendent of the chosen PAGE_OFFSET. 3. Memory consumed by initial page tables on RV64 system is 2 pages (i.e. 8 KB) which has significantly reduced and these pages will be freed as-part of the init memory free-up. The patch also provides a foundation for implementing strict kernel mappings where we protect kernel text and rodata using PTE permissions. Suggested-by: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Anup Patel <anup.patel@wdc.com> [paul.walmsley@sifive.com: updated to apply; fixed a checkpatch warning] Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Diffstat (limited to 'arch/riscv/include/asm/pgtable.h')
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 18ea56fabba8..a364aba23d55 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -59,6 +59,8 @@
#define PAGE_KERNEL __pgprot(_PAGE_KERNEL)
+#define PAGE_TABLE __pgprot(_PAGE_TABLE)
extern pgd_t swapper_pg_dir[];
/* MAP_PRIVATE permissions: xwr (copy-on-write) */
@@ -118,6 +120,11 @@ static inline pgd_t pfn_pgd(unsigned long pfn, pgprot_t prot)
return __pgd((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
+static inline unsigned long _pgd_pfn(pgd_t pgd)
+ return pgd_val(pgd) >> _PAGE_PFN_SHIFT;
#define pgd_index(addr) (((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
/* Locate an entry in the page global directory */
@@ -400,6 +407,7 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
#define kern_addr_valid(addr) (1) /* FIXME */
+extern void *dtb_early_va;
extern void setup_bootmem(void);
extern void paging_init(void);