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From:   Balbir Singh <bsingharora@gmail.com>
Date:   Wed, 6 Feb 2019 13:55:49 +1100
Message-ID: <CAKTCnzmC74fQ_NCGvvXY3sv--hp-C094jVy8JfCUYqwp_wcBAg@mail.gmail.com>
Subject: Re: [PATCH] powerpc/powernv/npu: Remove redundant change_pte() hook
To:     Alistair Popple <alistair@popple.id.au>
Cc:     Andrea Arcangeli <aarcange@redhat.com>,
        Peter Xu <peterx@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Alexey Kardashevskiy <aik@ozlabs.ru>,
        Mark Hairgrove <mhairgrove@nvidia.com>,
        David Gibson <david@gibson.dropbear.id.au>,
        Jerome Glisse <jglisse@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@lists.ozlabs.org>
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On Tue, Feb 5, 2019 at 2:52 PM Alistair Popple <alistair@popple.id.au> wrote:
>
> On Thursday, 31 January 2019 12:11:06 PM AEDT Andrea Arcangeli wrote:
> > On Thu, Jan 31, 2019 at 06:30:22PM +0800, Peter Xu wrote:
> > > The change_pte() notifier was designed to use as a quick path to
> > > update secondary MMU PTEs on write permission changes or PFN changes.
> > > For KVM, it could reduce the vm-exits when vcpu faults on the pages
> > > that was touched up by KSM.  It's not used to do cache invalidations,
> > > for example, if we see the notifier will be called before the real PTE
> > > update after all (please see set_pte_at_notify that set_pte_at was
> > > called later).
>
> Thanks for the fixup. I didn't realise that invalidate_range() always gets
> called but I now see that is the case so this change looks good to me as well.
>
> Reviewed-by: Alistair Popple <alistair@popple.id.au>
>
I checked the three callers of set_pte_at_notify and the assumption
seems correct

Reviewed-by: Balbir Singh <bsingharora@gmail.com>