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To:     Kristen Carlson Accardi <kristen@linux.intel.com>,
        Jarkko Sakkinen <jarkko@kernel.org>
Cc:     linux-sgx@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org
References: <20220107181618.6597-1-kristen@linux.intel.com>
 <20220107181618.6597-3-kristen@linux.intel.com> <Ydm2Qk8JFwgdueZa@iki.fi>
 <fda3bb7bd557a37112a4f7c6c205871addda1bd3.camel@linux.intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH v2 2/2] x86/sgx: account backing pages
Message-ID: <ed190b80-75cb-3137-1d64-1a87e1ac930e@intel.com>
Date:   Fri, 14 Jan 2022 09:55:51 -0800
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On 1/14/22 9:51 AM, Kristen Carlson Accardi wrote:
>>> +int sgx_encl_lookup_backing(struct sgx_encl *encl, unsigned long
>>> page_index,
>>> +			    struct sgx_backing *backing)
>>> +{
>>> +	return sgx_encl_get_backing(encl, page_index, backing);
>>> +}
>> IMHO, sgx_encl_backing() should be open-coded here.
> I can understand your hesitation, but I agree with Dave here that
> wrapping the function makes the code more clear. I would prefer to keep
> this the way it is.

I'd also like to see sgx_encl_lookup_backing() and
sgx_encl_alloc_backing() diverge more in the future.

For instance, sgx_encl_alloc_backing() could ensure that the page does
not exist in the file before doing the sgx_encl_get_backing() call.
This would ensure that it truly *does* allocate a page and does not just
return a previously-allocated page.

sgx_encl_lookup_backing() could ensure the opposite: that the page
*DOES* exist in the file before doing the sgx_encl_get_backing() call.
This would ensure that it does not allocate a page in a case where we
expected an old, existing page to be present.