From: Dave Hansen <dave.hansen@intel.com>
To: Reinette Chatre <reinette.chatre@intel.com>,
dave.hansen@linux.intel.com, jarkko@kernel.org,
linux-sgx@vger.kernel.org
Cc: haitao.huang@intel.com
Subject: Re: [RFC PATCH 0/4] SGX shmem backing store issue
Date: Wed, 4 May 2022 16:50:54 -0700 [thread overview]
Message-ID: <fd752d77-9f33-9618-36c1-66dee6c2e93c@intel.com> (raw)
In-Reply-To: <468848d0-ad58-8da0-dd39-b9604d458cdf@intel.com>
On 5/4/22 16:36, Reinette Chatre wrote:
> The page fault handler cannot check for SGX_ENCL_PAGE_BEING_RECLAIMED
> until the reclaimer releases the mutex.
Ahh, got it now. I thought the mutex wasn't held on the reclaimer side.
Thanks for the refresher.
>> One other thing. The role of encl->lock here is very important.
>> Without it, two concurrent page faults could do their individual
>> memset(), each see !pcmd_page_empty, then decline to truncate the page.
>
> Your argument is not clear to me. Yes, this would be an issue (and
> that will not be the only issue) if the enclave mutex is not held
> by the page fault handler ... but the enclave mutex _is_ held by the
> page fault handler.
It would just be nice to clearly state the locking logic in the eventual
changelog.
>> Also, given the challenges here, I do think we should check the
>> pcmd_page after truncate to ensure it is still all zero's.
>
> Could you please elaborate the challenges? I do not think it would
> help the issue at hand at all to add a check since this is done with
> the mutex held while the reclaimer has a reference to the page but no
> mutex ... as long as the page fault handler has that mutex it can write
> and check the PCMD page all it want, the new changes would occur to the
> PCMD page when it (the page fault handler) releases the mutex and the
> reclaimer attempts to use the page it has a reference to.
I'm just asking for a debugging check that looks at the page *after* is
has been truncated to ensure it is zero, in case another bug creeps in here.
next prev parent reply other threads:[~2022-05-05 0:01 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-28 20:11 [RFC PATCH 0/4] SGX shmem backing store issue Reinette Chatre
2022-04-28 20:11 ` [RFC PATCH 1/4] x86/sgx: Do not free backing memory on ENCLS[ELDU] failure Reinette Chatre
2022-04-28 21:30 ` Dave Hansen
2022-04-28 22:20 ` Reinette Chatre
2022-04-28 22:53 ` Dave Hansen
2022-04-28 23:49 ` Reinette Chatre
2022-05-03 2:01 ` Kai Huang
2022-05-07 17:25 ` Jarkko Sakkinen
2022-05-09 17:17 ` Reinette Chatre
2022-05-10 0:36 ` Kai Huang
2022-05-11 10:26 ` Jarkko Sakkinen
2022-05-11 18:29 ` Haitao Huang
2022-05-11 22:00 ` Kai Huang
2022-05-12 21:14 ` Jarkko Sakkinen
2022-05-06 22:09 ` Jarkko Sakkinen
2022-04-28 20:11 ` [RFC PATCH 2/4] x86/sgx: Set dirty bit after modifying page contents Reinette Chatre
2022-04-28 21:40 ` Dave Hansen
2022-04-28 22:41 ` Reinette Chatre
2022-05-06 22:27 ` Jarkko Sakkinen
2022-05-06 22:40 ` Reinette Chatre
2022-05-07 18:01 ` Jarkko Sakkinen
2022-04-28 20:11 ` [RFC PATCH 3/4] x86/sgx: Obtain backing storage page with enclave mutex held Reinette Chatre
2022-04-28 21:58 ` Dave Hansen
2022-04-28 22:44 ` Reinette Chatre
2022-05-06 22:43 ` Jarkko Sakkinen
2022-04-28 20:11 ` [RFC PATCH 4/4] x86/sgx: Do not allocate backing pages when loading from backing store Reinette Chatre
2022-04-28 21:12 ` [RFC PATCH 0/4] SGX shmem backing store issue Dave Hansen
2022-04-29 18:50 ` Reinette Chatre
2022-04-29 19:45 ` Dave Hansen
2022-04-30 3:22 ` Reinette Chatre
2022-04-30 15:52 ` Reinette Chatre
2022-05-02 14:36 ` Dave Hansen
2022-05-02 17:11 ` Reinette Chatre
2022-05-02 21:33 ` Dave Hansen
2022-05-04 22:13 ` Reinette Chatre
2022-05-04 22:58 ` Dave Hansen
2022-05-04 23:36 ` Reinette Chatre
2022-05-04 23:50 ` Dave Hansen [this message]
2022-05-05 0:08 ` Reinette Chatre
2022-05-04 23:05 ` Dave Hansen
2022-05-07 17:46 ` Jarkko Sakkinen
2022-05-07 17:48 ` Jarkko Sakkinen
2022-05-09 17:09 ` Reinette Chatre
2022-05-10 22:28 ` Jarkko Sakkinen
2022-05-11 17:23 ` Reinette Chatre
2022-05-12 14:10 ` Jarkko Sakkinen
2022-04-28 21:29 ` Dave Hansen
2022-04-28 22:20 ` Reinette Chatre
2022-05-04 6:40 ` Jarkko Sakkinen
2022-05-05 6:09 ` Jarkko Sakkinen
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