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Date:   Sat, 15 Jan 2022 01:57:09 +0200
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Kristen Carlson Accardi <kristen@linux.intel.com>,
        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
Subject: Re: [PATCH v2 2/2] x86/sgx: account backing pages
Message-ID: <YeIN1RQydD1juJGA@iki.fi>
References: <20220107181618.6597-1-kristen@linux.intel.com>
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 <Ydm2Qk8JFwgdueZa@iki.fi>
 <fda3bb7bd557a37112a4f7c6c205871addda1bd3.camel@linux.intel.com>
 <ed190b80-75cb-3137-1d64-1a87e1ac930e@intel.com>
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On Fri, Jan 14, 2022 at 09:55:51AM -0800, Dave Hansen wrote:
> 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.

Would it be a too big tretch to add these and make the whole scheme
fully legit? Does not sound like an extremely huge stretch and there is now
a full cycle amount of time make it happen before 5.18 merge window.

/Jarkko