Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Julia Lawall <julia.lawall@inria.fr>, ira.weiny@intel.com
Cc:     Alaa Mohamed <eng.alaamohamedsoliman.am@gmail.com>,
        outreachy@lists.linux.dev, boris.ostrovsky@oracle.com,
        jgross@suse.com, sstabellini@kernel.org,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] xen:  Convert kmap() to kmap_local_page()
Date:   Wed, 20 Apr 2022 15:55:34 +0200
Message-ID: <3990312.6PsWsQAL7t@leap>
In-Reply-To: <alpine.DEB.2.22.394.2204201538560.2937@hadrien>
References: <20220419234328.10346-1-eng.alaamohamedsoliman.am@gmail.com> <2940450.687JKscXgg@leap> <alpine.DEB.2.22.394.2204201538560.2937@hadrien>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset="utf-8"
Precedence: bulk

On mercoled=C3=AC 20 aprile 2022 15:40:10 CEST Julia Lawall wrote:
>=20
> On Wed, 20 Apr 2022, Fabio M. De Francesco wrote:
>=20
> > On mercoled=C3=AC 20 aprile 2022 08:03:05 CEST Julia Lawall wrote:
> > >
> > > On Wed, 20 Apr 2022, Alaa Mohamed wrote:
> > >
> > > > kmap() is being deprecated and these usages are all local to the=20
thread
> > > > so there is no reason kmap_local_page() can't be used.
> > > >
> > > > Replace kmap() calls with kmap_local_page().
> > >
> > > OK, so from a Coccinelle point of view, could we do
> > >
> > > @@
> > > expression e1,e2,x,f;
> > > @@
> > >
> > > e1 =3D
> > > - kmap
> > > + kmap_local_page
> > >     (e2)
> > > ... when !=3D x =3D e1 // not stored in any location and not passed to
> > another function
> > >     when !=3D f(...,e1,...)
> > >     when !=3D x =3D e2
> > >     when !=3D f(...,e2,...)
> > > -kunmap(e2)
> > > +kunmap_local(e1)
> > >
> > > julia
> > >
> >
> > I've never spent sufficient time to understand properly the syntax and
> > semantics of expressions of Coccinelle. However, thanks Julia, this=20
code
> > looks good and can be very helpful.
> >
> > Only a minor objection... it doesn't tell when 'e2' has been allocated
> > within the same function where the kmap() call is.
> >
> > In the particular case that I cite above, I'd prefer to remove the
> > allocation of the page (say with alloc_page()) and convert kmap() /
kunmap()
> > to use kmalloc() / kfree().
> >
> > Fox example, this is done in the following patch:
> >
> > commit 633b0616cfe0 ("x86/sgx: Remove unnecessary kmap() from
> > sgx_ioc_enclave_init()") from Ira Weiny.
> >
> > Can Coccinelle catch also those special cases where a page that is=20
passed
> > to kmap() is allocated within that same function (vs. being passed as
> > argument to this function) and, if so, propose a replacement with
> > kmalloc()?
>=20
> It looks complex in this case, because the allocation is in another
> function, and it is passed to another function.

This is not the special case I was talking about. In this case your code=20
for Coccinelle tells the right proposal and it is exactly what Alaa did in=
=20
her patch (which is good!).

I'm talking about other special cases like the one I pointed to with the=20
link I provided. I'm sorry if my bad English made you think that Alaa's=20
patch was one of those cases where the page is allocated within the same=20
function where kmap() is.

I hope that now I've been clearer :)

Thanks,

=46abio