linux-kernel - Re: [RFC PATCH 4/6] x86/mm/tlb: Refactor common code into flush_tlb_on

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Message-ID: <20190527092434.GT2623@hirez.programming.kicks-ass.net>
Date:   Mon, 27 May 2019 11:24:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [RFC PATCH 4/6] x86/mm/tlb: Refactor common code into
 flush_tlb_on_cpus()

On Sat, May 25, 2019 at 01:22:01AM -0700, Nadav Amit wrote:

> There is one functional change, which should not affect correctness:
> flush_tlb_mm_range compared loaded_mm and the mm to figure out if local
> flush is needed. Instead, the common code would look at the mm_cpumask()
> which should give the same result.

> @@ -786,18 +804,9 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
>  	info = get_flush_tlb_info(mm, start, end, stride_shift, freed_tables,
>  				  new_tlb_gen);
>  
> -	if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
> -		lockdep_assert_irqs_enabled();
> -		local_irq_disable();
> -		flush_tlb_func_local(info, TLB_LOCAL_MM_SHOOTDOWN);
> -		local_irq_enable();
> -	}
> -
> -	if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids)
> -		flush_tlb_others(mm_cpumask(mm), info);

So if we want to double check that; we'd add:

	WARN_ON_ONCE(cpumask_test_cpu(smp_processor_id(), mm_cpumask(mm)) ==
		     (mm == this_cpu_read(cpu_tlbstate.loaded_mm)));

right?

> +	flush_tlb_on_cpus(mm_cpumask(mm), info);
>  
>  	put_flush_tlb_info();
> -	put_cpu();
>  }