linux-kernel - Re: [PATCH] powerpc/powernv/npu: Remove redundant change

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Date:   Wed, 6 Feb 2019 13:55:49 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Alistair Popple <alistair@...ple.id.au>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Mark Hairgrove <mhairgrove@...dia.com>,
        David Gibson <david@...son.dropbear.id.au>,
        Jerome Glisse <jglisse@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] powerpc/powernv/npu: Remove redundant change_pte() hook

On Tue, Feb 5, 2019 at 2:52 PM Alistair Popple <alistair@...ple.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@...ple.id.au>
>
I checked the three callers of set_pte_at_notify and the assumption
seems correct

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