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

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Message-ID: <CAAhSdy3KLCW540mLVk4F6nAqYP2dYuiGqO4FuwTD1Hra_gHcGg@mail.gmail.com>
Date:   Mon, 19 Aug 2019 20:39:02 +0530
From:   Anup Patel <anup@...infault.org>
To:     "hch@...radead.org" <hch@...radead.org>
Cc:     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 8:16 PM hch@...radead.org <hch@...radead.org> wrote:
>
> On Thu, Aug 15, 2019 at 08:37:04PM +0000, Atish Patra wrote:
> > We get ton of them. Here is the stack dump.
>
> Looks like we might not need to flush anything at all here as the
> mm_struct was never scheduled to run on any cpu?

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.

Regards,
Anup