linux-kernel - Re: [PATCH v2 02/18] x86/sgx: Store struct sgx

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Message-ID: <2015ae96-5459-1f82-596b-f46af08ef766@intel.com>
Date:   Fri, 2 Dec 2022 13:48:32 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>,
        jarkko@...nel.org, dave.hansen@...ux.intel.com, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:     zhiquan1.li@...el.com, Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v2 02/18] x86/sgx: Store struct sgx_encl when allocating
 new VA pages

On 12/2/22 13:40, Kristen Carlson Accardi wrote:
> On Fri, 2022-12-02 at 13:35 -0800, Dave Hansen wrote:
>> On 12/2/22 10:36, Kristen Carlson Accardi wrote:
>>> When allocating new Version Array (VA) pages, pass the struct
>>> sgx_encl
>>> of the enclave that is allocating the page. sgx_alloc_epc_page()
>>> will
>>> store this value in the encl_owner field of the struct
>>> sgx_epc_page. In
>>> a later patch, VA pages will be placed in an unreclaimable queue,
>>> and then when the cgroup max limit is reached and there are no more
>>> reclaimable pages and the enclave must be oom killed, all the
>>> VA pages associated with that enclave can be uncharged and freed.
>> What does this have to do with the 'encl' that is being passed,
>> though?
>>
>> In other words, why is this new sgx_epc_page-to-encl mapping needed
>> for
>> VA pages now, but it wasn't before?
> When we OOM kill an enclave, we want to get rid of all the associated
> VA pages too. Prior to this patch, there wasn't a way to easily get the
> VA pages associated with an enclave.

Given an enclave, we have encl->va_pages to look up all the VA pages.
Also, this patch's code allows you to go from a va page to an enclave.
That seems like it's going the other direction from what an OOM-kill
would need to do.