RISC-V: mm: Fix set_satp_mode() for platform not having Sv57

When Sv57 is not available the satp.MODE test in set_satp_mode() will
fail and lead to pgdir re-programming for Sv48. The pgdir re-programming
will fail as well due to pre-existing pgdir entry used for Sv57 and as
a result kernel fails to boot on RISC-V platform not having Sv57.

To fix above issue, we should clear the pgdir memory in set_satp_mode()
before re-programming.

Fixes: 011f09d120 ("riscv: mm: Set sv57 on defaultly")
Reported-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/mm/init.c

@@ -718,6 +718,7 @@ retry:
 		if (!check_l4) {
 			disable_pgtable_l5();
 			check_l4 = true;
+			memset(early_pg_dir, 0, PAGE_SIZE);
 			goto retry;
 		}
 		disable_pgtable_l4();