RISC-V: Avoid using invalid intermediate translations
This is almost entirely a comment.
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 987d464..370c66c 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -96,7 +96,9 @@
/*
* Load trampoline page directory, which will cause us to trap to
- * stvec if VA != PA, or simply fall through if VA == PA
+ * stvec if VA != PA, or simply fall through if VA == PA. We need a
+ * full fence here because setup_vm() just wrote these PTEs and we need
+ * to ensure the new translations are in use.
*/
la a0, trampoline_pg_dir
srl a0, a0, PAGE_SHIFT
@@ -115,8 +117,14 @@
la gp, __global_pointer$
.option pop
- /* Switch to kernel page tables */
+ /*
+ * Switch to kernel page tables. A full fence is necessary in order to
+ * avoid using the trampoline translations, which are only correct for
+ * the first superpage. Fetching the fence is guarnteed to work
+ * because that first superpage is translated the same way.
+ */
csrw CSR_SATP, a2
+ sfence.vma
ret
