Re: [PATCH] RISC-V: Issue a local tlb flush if possible.

[Atish Patra]

On Mon, 2019-08-12 at 07:56 -0700, Christoph Hellwig wrote:
> I agree with the comment that we really should move this out of line
> now, and 

sure.

> also that we can simplify it further, which also includes
> not bothering with the SBI call if we were the only online CPU.

I already had that optimization in my patch.

> I also thing we need to use get_cpu/put_cpu to be preemption safe.
> 
ok. I will update that.

> Also why would we need to do a local flush if we have a mask that
> doesn't include the local CPU?
> 

I thought if it recieves an empty cpumask, then it should at least do a
local flush is the expected behavior. Are you saying that we should
just skip all and return ? 


> How about something like:
> 
> void __riscv_flush_tlb(struct cpumask *cpumask, unsigned long start,
> 		unsigned long size)
> {
> 	unsigned int cpu;
> 
> 	if (!cpumask)
> 		cpumask = cpu_online_mask;
> 
> 	cpu = get_cpu();
> 	if (!cpumask || cpumask_test_cpu(cpu, cpumask) {
> 		if ((start == 0 && size == -1) || size > PAGE_SIZE)
> 			local_flush_tlb_all();
> 		else if (size == PAGE_SIZE)
> 			local_flush_tlb_page(start);
> 		cpumask_clear_cpu(cpuid, cpumask);

This will modify the original cpumask which is not correct. clear part
has to be done on hmask to avoid a copy.

Regards,
Atish
> 	}
> 
> 	if (!cpumask_empty(cpumask)) {
> 	  	struct cpumask hmask;
> 
> 		riscv_cpuid_to_hartid_mask(cpumask, &hmask);
> 		sbi_remote_sfence_vma(hmask.bits, start, size);
> 	}
> 	put_cpu();
> }