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Subject: Re: [PATCH 1/4] x86/sgx: Track phase and type of SGX EPC pages
To:     "Luck, Tony" <tony.luck@intel.com>
CC:     Jarkko Sakkinen <jarkko@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20210708181423.1312359-1-tony.luck@intel.com>
 <20210708181423.1312359-2-tony.luck@intel.com>
 <93845f78-120d-7522-bd3e-fe042380d29e@intel.com>
 <31668f36583844cbbae0b10a594193d6@intel.com>
From:   Reinette Chatre <reinette.chatre@intel.com>
Message-ID: <00114991-9075-84f4-797d-f0f953d34660@intel.com>
Date:   Wed, 14 Jul 2021 14:21:39 -0700
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Hi Tony,

On 7/14/2021 1:59 PM, Luck, Tony wrote:
>> Could this tracking be done at the enclave page (struct sgx_encl_page)
>> instead?
> 
> In principle yes. Though Sean has some issues with me tracking types
> at all.

For the SGX2 work knowing the page types are useful. Some instructions 
only work on certain page types and knowing beforehand whether an 
instruction could work helps to avoid dealing with the errors when it 
does not work.

>> The enclave page's EPC page information is not available when
>> the page is in swap and it would be useful to know the page type without
>> loading the page from swap. The information would continue to be
>> accessible from struct epc_page via the owner pointer that may make some
>> of the changes easier since it would not be needed to pass the page type
>> around so much and thus possibly address the SECS page issue that Sean
>> pointed out in
>> https://lore.kernel.org/lkml/YO3FuBupQTKYaKBf@google.com/
> 
> I think I noticed that the "owner" pointer in sgx_encl_page doesn't point
> back to the epc_page for all types of SGX pages. So some additional
> changes would be needed. I'm not at all sure why this is different (or
> what use the non-REG pages use "owner" for.

This may be VA pages? struct sgx_va_page also contains a pointer to an 
EPC page. I did not consider that for this case. Perhaps these could be 
identified uniquely.

Reinette