riscv: Use global mappings for kernel pages

We map kernel pages into all addresses spages, so they can be marked as
global.  This allows hardware to avoid flushing the kernel mappings when
moving between address spaces.

Signed-off-by: Guo Ren <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
[Palmer: commit text]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: guoren83

arch/riscv/include/asm/pgtable.h

@@ -134,7 +134,8 @@
 				| _PAGE_WRITE \
 				| _PAGE_PRESENT \
 				| _PAGE_ACCESSED \
-				| _PAGE_DIRTY)
+				| _PAGE_DIRTY \
+				| _PAGE_GLOBAL)
 
 #define PAGE_KERNEL		__pgprot(_PAGE_KERNEL)
 #define PAGE_KERNEL_READ	__pgprot(_PAGE_KERNEL & ~_PAGE_WRITE)