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

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Message-ID: <20190819151015.GA3316@infradead.org>
Date:   Mon, 19 Aug 2019 08:10:17 -0700
From:   "hch@...radead.org" <hch@...radead.org>
To:     Anup Patel <anup@...infault.org>
Cc:     "hch@...radead.org" <hch@...radead.org>,
        Atish Patra <Atish.Patra@....com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Anup Patel <Anup.Patel@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexios.zavras@...el.com" <alexios.zavras@...el.com>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "allison@...utok.net" <allison@...utok.net>
Subject: Re: [PATCH] RISC-V: Issue a local tlb flush if possible.

On Mon, Aug 19, 2019 at 08:39:02PM +0530, Anup Patel wrote:
> If we were using ASID then yes we don't need to flush anything
> but currently we don't use ASID due to lack of HW support and
> HW can certainly do speculatively page table walks so flushing
> local TLB when MM mask is empty might help.
> 
> This just my theory and we need to stress test more.

Well, when we context switch away from a mm we always flush the
local tlb.  So either the mm_struct has never been scheduled in,
or we alrady did a local_tlb_flush and we context switched it up.