linux-kernel - Re: [PATCH V4 14/31] x86/sgx: Support VA page allocation without reclaiming

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Date:   Fri, 15 Apr 2022 08:54:53 -0500
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "Jarkko Sakkinen" <jarkko@...nel.org>, dave.hansen@...ux.intel.com,
        tglx@...utronix.de, bp@...en8.de, luto@...nel.org,
        mingo@...hat.com, linux-sgx@...r.kernel.org, x86@...nel.org,
        shuah@...nel.org, linux-kselftest@...r.kernel.org,
        "Reinette Chatre" <reinette.chatre@...el.com>
Cc:     seanjc@...gle.com, kai.huang@...el.com, cathy.zhang@...el.com,
        cedric.xing@...el.com, haitao.huang@...el.com,
        mark.shanahan@...el.com, vijay.dhanraj@...el.com, hpa@...or.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 14/31] x86/sgx: Support VA page allocation without
 reclaiming

On Thu, 14 Apr 2022 11:30:34 -0500, Reinette Chatre  
<reinette.chatre@...el.com> wrote:

> Hi Jarkko,
>
> On 4/14/2022 4:18 AM, Jarkko Sakkinen wrote:
>> On Wed, 2022-04-13 at 14:10 -0700, Reinette Chatre wrote:
>>> struct sgx_encl should be protected with the mutex
>>> sgx_encl->lock. One exception is sgx_encl->page_cnt that
>>> is incremented (in sgx_encl_grow()) when an enclave page
>>> is added to the enclave. The reason the mutex is not held
>>> is to allow the reclaimer to be called directly if there are
>>> no EPC pages (in support of a new VA page) available at the time.
>>>
>>> Incrementing sgx_encl->page_cnt without sgc_encl->lock held
>>> is currently (before SGX2) safe from concurrent updates because
>>> all paths in which sgx_encl_grow() is called occur before
>>> enclave initialization and are protected with an atomic
>>> operation on SGX_ENCL_IOCTL.
>>>
>>> SGX2 includes support for dynamically adding pages after
>>> enclave initialization where the protection of SGX_ENCL_IOCTL
>>> is not available.
>>>
>>> Make direct reclaim of EPC pages optional when new VA pages
>>> are added to the enclave. Essentially the existing "reclaim"
>>> flag used when regular EPC pages are added to an enclave
>>> becomes available to the caller when used to allocate VA pages
>>> instead of always being "true".
>>>
>>> When adding pages without invoking the reclaimer it is possible
>>> to do so with sgx_encl->lock held, gaining its protection against
>>> concurrent updates to sgx_encl->page_cnt after enclave
>>> initialization.
>>>
>>> No functional change.
>>>
>>> Reported-by: Haitao Huang <haitao.huang@...el.com>
>>> Tested-by: Haitao Huang <haitao.huang@...el.com>
>>> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
>>
>> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
>
> Thank you.
>
>>
>> Nit: I don't think tested-by is in the right patch here. Maybe
>> Haitao's tested-by should be moved into patch that actually adds
>> support for EAUG? Not something I would NAK this patch, just
>> wondering...
>
> Yes, that is a good point. While this is the bulk of the fix where
> the new API is introduced, the test is only applicable when this API
> is used and that is in "x86/sgx: Support adding of pages to an
> initialized enclave". I will move the "Tested-by" to that patch.
>

You can also add my Tested-by for patches adding the new IOCTLs.
Our team and I have tested EAUG on #PF,  modifying types and permissions  
with Intel SGX SDK/PSW.
Thanks
Haitao