riscv: Fix huge_ptep_set_wrprotect when PTE is a NAPOT

We need to avoid inconsistencies across the PTEs that form a NAPOT
region, so when we write protect such a region, we should clear and flush
all the PTEs to make sure that any of those PTEs is not cached which would
result in such inconsistencies (arm64 does the same).

Fixes: 82a1a1f3

 ("riscv: mm: support Svnapot in hugetlb page")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20230428120120.21620-1-alexghiti@rivosinc.com


Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>