RISC-V: only flush icache when it has VM_EXEC set

As I-Cache flush on current RISC-V needs to send IPIs to every CPU cores
in the system is very costly, limiting flush_icache_mm to be called only
when vma->vm_flags has VM_EXEC can help minimize the frequency of these
operations. It improves performance and reduces disturbances when
copy_from_user_page is needed such as profiling with perf.

For I-D coherence concerns, it will not fail if such a page adds VM_EXEC
flags in the future since we have checked it in the __set_pte_at function.

Signed-off-by: Yangyu Chen <cyy@cyyself.name>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/tencent_6D851035F6F2FD0B5A69FB391AE39AC6300A@qq.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/cacheflush.h

@@ -33,8 +33,11 @@ static inline void flush_dcache_page(struct page *page)
  * so instead we just flush the whole thing.
  */
 #define flush_icache_range(start, end) flush_icache_all()
-#define flush_icache_user_page(vma, pg, addr, len) \
-	flush_icache_mm(vma->vm_mm, 0)
+#define flush_icache_user_page(vma, pg, addr, len)	\
+do {							\
+	if (vma->vm_flags & VM_EXEC)			\
+		flush_icache_mm(vma->vm_mm, 0);		\
+} while (0)
 
 #ifdef CONFIG_64BIT
 #define flush_cache_vmap(start, end)		flush_tlb_kernel_range(start, end)