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Date:   Tue, 13 Aug 2019 07:30:27 -0700
From:   "hch@infradead.org" <hch@infradead.org>
To:     Atish Patra <Atish.Patra@wdc.com>
Cc:     "hch@infradead.org" <hch@infradead.org>,
        "aou@eecs.berkeley.edu" <aou@eecs.berkeley.edu>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        Anup Patel <Anup.Patel@wdc.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "alexios.zavras@intel.com" <alexios.zavras@intel.com>,
        "palmer@sifive.com" <palmer@sifive.com>,
        "paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        "allison@lohutok.net" <allison@lohutok.net>
Subject: Re: [PATCH] RISC-V: Issue a local tlb flush if possible.
Message-ID: <20190813143027.GA31668@infradead.org>
References: <20190810014309.20838-1-atish.patra@wdc.com>
 <20190812145631.GC26897@infradead.org>
 <f58814e156b918531f058acfac944abef34f5fb1.camel@wdc.com>
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On Tue, Aug 13, 2019 at 12:15:15AM +0000, Atish Patra wrote:
> 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 could we ever receive an empty cpu mask?  I think it could only
be empty without the current cpu.  At least that is my reading of
the callers and a few other implementations.

> > 	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.

Indeed.  But looking at the x86 tlbflush implementation it seems like we
could use cpumask_any_but() to avoid having to modify the passed in
cpumask.