RISC-V: Do not invoke SBI call if cpumask is empty

SBI calls are expensive. If cpumask is empty, there is no need to
trap via SBI as no remote tlb flushing is required.

Signed-off-by: Atish Patra <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Paul Walmsley <[email protected]>

Author: atishp04

arch/riscv/mm/tlbflush.c

@@ -14,6 +14,9 @@ static void __sbi_tlb_flush_range(struct cpumask *cmask, unsigned long start,
 {
 	struct cpumask hmask;
 
+	if (cpumask_empty(cmask))
+		return;
+
 	riscv_cpuid_to_hartid_mask(cmask, &hmask);
 	sbi_remote_sfence_vma(hmask.bits, start, size);
 }