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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Ira Weiny <ira.weiny@intel.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Peter Collingbourne <pcc@google.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/highmem: VM_BUG_ON() if offset + len > PAGE_SIZE
Date:   Tue, 26 Apr 2022 23:10:44 +0200
Message-ID: <5262074.Sb9uPGUboI@leap>
In-Reply-To: <20220426134811.63a398ea5d2212dfececfd83@linux-foundation.org>
References: <20220426193020.8710-1-fmdefrancesco@gmail.com> <1790890.atdPhlSkOF@leap> <20220426134811.63a398ea5d2212dfececfd83@linux-foundation.org>
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On marted=C3=AC 26 aprile 2022 22:48:11 CEST Andrew Morton wrote:
> On Tue, 26 Apr 2022 22:19:57 +0200 "Fabio M. De Francesco"=20
<fmdefrancesco@gmail.com> wrote:
>=20
> > On marted=C3=AC 26 aprile 2022 21:34:12 CEST Andrew Morton wrote:
> > > On Tue, 26 Apr 2022 21:30:20 +0200 "Fabio M. De Francesco"=20
> > <fmdefrancesco@gmail.com> wrote:
> > >=20
> > > > Add VM_BUG_ON() bounds checking to make sure that, if "offset +=20
len>
> > > > PAGE_SIZE", memset() does not corrupt data in adjacent pages.
> > > >=20
> > >=20
> > > hm, why?  To match all the other functions in there?
> > >=20
> > > I suppose that's logical.  Or we could just delete all the other
> > > VM_BUG_ON()s.  Have any of them proven to be at all useful?
> > >=20
> > I am not so sure about it being so useful. I just noted that=20
memzero_page()=20
> > is the only function of that family that is implemented with no=20
> > VM_BUG_ON(). I have no actual proofs of usefulness :(=20
> >=20
> > This is why yesterday I sent an "RFC Patch" (please see =20
> > https://lore.kernel.org/lkml/20220424104806.25396-1-fmdefrancesco@gmail=
=2Ecom/
> >=20
> > Soon after sending it I thought that VM_WARN_ON_ONCE() could have been=
=20
> > better suited, but Ira Weiny wrote to use VM_BUG_ON() for consistency.
> >=20
> > Now I could either delete all other VM_BUG_ON() or replace them with=20
> > VM_WARN_ON_ONCE() (or some other macro).=20
> >=20
> > Ah, a third solution might be to leave highmem.h as it is now :)
> >=20
> > What do you prefer?
>=20
> Merge this patch as-is, I guess.  Going through and removing unuseful
> VM_BUG_ON()s is a separable activity.
>=20
Thanks!

While at this, I've just noted that you sent a confirmation which lists all=
=20
the patches of mine that are currently in your tree.

I see that you took v1 of "Extend and reorganize Highmem's documentation".=
=20
I suppose that you missed the v2 of that series at
https://lore.kernel.org/lkml/20220425162400.11334-1-fmdefrancesco@gmail.com=
/=20

Can you please check it?

Thanks,

=46abio