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Message-ID: <931e05840165b8285acf8d13ded01fb233b6549c.camel@kernel.org>
Subject: Re: [PATCH v5 1/7] x86/sgx: Provide indication of life-cycle of EPC
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From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Dave Hansen <dave.hansen@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Sean Christopherson <seanjc@google.com>
Cc:     Cathy Zhang <cathy.zhang@intel.com>, linux-sgx@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 22 Sep 2021 08:27:58 +0300
In-Reply-To: <057511a3-3bc8-f073-e0f8-7b14646f82fe@intel.com>
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         <20210917213836.175138-2-tony.luck@intel.com>
         <bba7e537fd9197a92358640ebb0aef365984cebc.camel@kernel.org>
         <057511a3-3bc8-f073-e0f8-7b14646f82fe@intel.com>
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On Tue, 2021-09-21 at 15:15 -0700, Dave Hansen wrote:
> On 9/21/21 2:28 PM, Jarkko Sakkinen wrote:
> > > Since there are multiple uses of the "owner" field with different typ=
es
> > > change the sgx_epc_page structure to define an anonymous union with
> > > each of the uses explicitly called out.
> > But it's still always a pointer.
> >=20
> > And not only that, but two alternative fields in that union have *exact=
ly* the
> > same type, so it's kind of artifically representing the problem more co=
mplex
> > than it really is.
> >=20
> > I'm not just getting, why all this complexity, and not a few casts inst=
ead?
>=20
> I suggested this.  It makes the structure more self-describing because
> it explicitly lists the possibles uses of the space in the structure.
>=20
> Maybe I stare at 'struct page' and its 4 unions too much and I'm
> enamored by their shininess.  But, in the end, I prefer unions to casting=
.

Yeah, packing data into constrained space (as in the case of struct page) i=
s
the only application for, where you can speak of a quantitative decision, w=
hen
you pick union.

/Jarkko