linux-kernel - Re: [PATCH v3 07/17] arm64, hibernate: move page handling function to new trans

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Message-ID: <CA+CK2bDTVGm6pNRGQx7eAyEP6m0xr9X1No_=qgUOTDAoL9uigw@mail.gmail.com>
Date:   Fri, 6 Sep 2019 13:41:17 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     James Morse <james.morse@....com>
Cc:     James Morris <jmorris@...ei.org>, Sasha Levin <sashal@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        kexec mailing list <kexec@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>, will@...nel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        linux-mm <linux-mm@...ck.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v3 07/17] arm64, hibernate: move page handling function to
 new trans_pgd.c

On Fri, Sep 6, 2019 at 11:18 AM James Morse <james.morse@....com> wrote:
>
> Hi Pavel,
>
> On 21/08/2019 19:31, Pavel Tatashin wrote:
> > Now, that we abstracted the required functions move them to a new home.
> > Later, we will generalize these function in order to be useful outside
> > of hibernation.
>
> > diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
> > new file mode 100644
> > index 000000000000..00b62d8640c2
> > --- /dev/null
> > +++ b/arch/arm64/mm/trans_pgd.c
> > @@ -0,0 +1,211 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/*
> > + * Copyright (c) 2019, Microsoft Corporation.
> > + * Pavel Tatashin <patatash@...ux.microsoft.com>
>
> Hmmm, while line-count isn't a useful metric: this file contains 41% of the code that was
> in hibernate.c, but has stripped the substantial copyright-pedigree that the hibernate
> code had built up over the years.
> (counting lines identified by 'cloc' as code, not comments or blank)
>
> If you are copying or moving a non trivial quantity of code, you need to preserve the
> copyright. Something like 'Derived from the arm64 hibernate support which has:'....

I will do that.  The copyright thing was meant to appear in
"generalization" patch that comes later, where I unified most of the
code to be symmetric.
So, I will add it there, and also do the derived message that you suggested.

>
>
> > + */
> > +
> > +/*
> > + * Transitional tables are used during system transferring from one world to
> > + * another: such as during hibernate restore, and kexec reboots. During these
> > + * phases one cannot rely on page table not being overwritten.
>
> I think you need to mention that hibernate and kexec are rewriting memory, and may
> overwrite the live page tables, therefore ...

Will add, thank you.

Pasha