[PATCH v4 3/6] riscv: Move DTB_EARLY_BASE_VA to the kernel address space

[Alexandre Ghiti]

The early virtual address should lie in the kernel address space for
inline kasan instrumentation to succeed, otherwise kasan tries to
dereference an address that does not exist in the address space (since
kasan only maps *kernel* address space, not the userspace).

Simply use the very first address of the kernel address space for the
early fdt mapping.

It allowed an Ubuntu kernel to boot successfully with inline
instrumentation.

Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.com>
---
 arch/riscv/mm/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 478d6763a01a..87f6a5d475a6 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -57,7 +57,7 @@ unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
 EXPORT_SYMBOL(empty_zero_page);
 
 extern char _start[];
-#define DTB_EARLY_BASE_VA      PGDIR_SIZE
+#define DTB_EARLY_BASE_VA      (ADDRESS_SPACE_END - (PTRS_PER_PGD / 2 * PGDIR_SIZE) + 1)
 void *_dtb_early_va __initdata;
 uintptr_t _dtb_early_pa __initdata;
 
-- 
2.37.2