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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 15:22:10 +0200
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In-Reply-To: <alpine.DEB.2.22.394.2204200759080.2937@hadrien>
References: <20220419234328.10346-1-eng.alaamohamedsoliman.am@gmail.com> <alpine.DEB.2.22.394.2204200759080.2937@hadrien>
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On mercoled=C3=AC 20 aprile 2022 08:03:05 CEST Julia Lawall wrote:
>=20
> On Wed, 20 Apr 2022, Alaa Mohamed wrote:
>=20
> > kmap() is being deprecated and these usages are all local to the thread
> > so there is no reason kmap_local_page() can't be used.
> >
> > Replace kmap() calls with kmap_local_page().
>=20
> OK, so from a Coccinelle point of view, could we do
>=20
> @@
> expression e1,e2,x,f;
> @@
>=20
> e1 =3D
> - kmap
> + kmap_local_page
>     (e2)
> ... when !=3D x =3D e1 // not stored in any location and not passed to=20
another function
>     when !=3D f(...,e1,...)
>     when !=3D x =3D e2
>     when !=3D f(...,e2,...)
> -kunmap(e2)
> +kunmap_local(e1)
>=20
> julia
>=20

I've never spent sufficient time to understand properly the syntax and=20
semantics of expressions of Coccinelle. However, thanks Julia, this code=20
looks good and can be very helpful.

Only a minor objection... it doesn't tell when 'e2' has been allocated=20
within the same function where the kmap() call is.

In the particular case that I cite above, I'd prefer to remove the=20
allocation of the page (say with alloc_page()) and convert kmap() /kunmap()=
=20
to use kmalloc() / kfree().=20

=46ox example, this is done in the following patch:

commit 633b0616cfe0 ("x86/sgx: Remove unnecessary kmap() from=20
sgx_ioc_enclave_init()") from Ira Weiny.

Can Coccinelle catch also those special cases where a page that is passed=20
to kmap() is allocated within that same function (vs. being passed as=20
argument to this function) and, if so, propose a replacement with=20
kmalloc()?

Thanks,

=46abio