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Message-ID: <d0789485cc353a99e19c2d2ca4b5a628a33a312d.camel@linux.ibm.com>
Subject: Re: [PATCH v6 02/11] mm/gup: Use functions to track lockless pgtbl
 walks on gup_pgd_range
From:   Leonardo Bras <leonardo@linux.ibm.com>
To:     John Hubbard <jhubbard@nvidia.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Steven Price <steven.price@arm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
        Balbir Singh <bsingharora@gmail.com>,
        Reza Arbab <arbab@linux.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Allison Randal <allison@lohutok.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Michal Suchanek <msuchanek@suse.de>
Cc:     linux-arch@vger.kernel.org, linux-mm@kvack.org,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        kvm-ppc@vger.kernel.org
Date:   Mon, 17 Feb 2020 17:55:49 -0300
In-Reply-To: <0c2f5a89-4890-fd84-6a6d-e470ba110399@nvidia.com>
References: <20200206030900.147032-1-leonardo@linux.ibm.com>
         <20200206030900.147032-3-leonardo@linux.ibm.com>
         <760c238043196e0628c8c0eff48a8e938ef539ba.camel@linux.ibm.com>
         <0c2f5a89-4890-fd84-6a6d-e470ba110399@nvidia.com>
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Hello John, comments inline;

On Fri, 2020-02-07 at 14:54 -0800, John Hubbard wrote:
> On 2/5/20 7:25 PM, Leonardo Bras wrote:
> > On Thu, 2020-02-06 at 00:08 -0300, Leonardo Bras wrote:
> > >                 gup_pgd_range(addr, end, gup_flags, pages, &nr);
> > > -               local_irq_enable();
> > > +               end_lockless_pgtbl_walk(IRQS_ENABLED);
> > >                 ret =3D nr;
> > >         }
> > > =20
> >=20
> > Just noticed IRQS_ENABLED is not available on other archs than ppc64.
> > I will fix this for v7.
> >=20
>=20
> What's the fix going to look like, approximately?

I am not sure what is the best approach yet.=20

1. On irq_mask =3D=3D 0, always enable irq on end_lockless_pgtbl_walk().
   Not sure how bat would that affect other archs.

2. Add another function like end_lockless_pgtbl_walk_irqen() that
always enables IRQ.

3. Add another parameter in end_lockless_pgtbl_walk(), so that caller
can choose ii IRQ must be enabled.

Also, not sure if internal_get_user_pages_fast() can possibly be called
with IRQ disabled, and then return with it enabled. Maybe just
saving/restoring should be fine.

Other suggestions are welcome.

>=20
>=20
> thanks,

Best regards,

Leonardo Bras

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