linux-kernel - Re: [PATCH v2] x86/sgx: Set active memcg prior to shmem allocation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YobMRaJBS1/FsQQG@kroah.com>
Date:   Fri, 20 May 2022 01:01:25 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc:     linux-sgx@...r.kernel.org, Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mhocko@...e.com, roman.gushchin@...ux.dev,
        hannes@...xchg.org, shakeelb@...gle.com
Subject: Re: [PATCH v2] x86/sgx: Set active memcg prior to shmem allocation

On Thu, May 19, 2022 at 02:04:45PM -0700, Kristen Carlson Accardi wrote:
> When the system runs out of enclave memory, SGX can reclaim EPC pages
> by swapping to normal RAM. These backing pages are allocated via a
> per-enclave shared memory area. Since SGX allows unlimited over
> commit on EPC memory, the reclaimer thread can allocate a large
> number of backing RAM pages in response to EPC memory pressure.
> 
> When the shared memory backing RAM allocation occurs during
> the reclaimer thread context, the shared memory is charged to
> the root memory control group, and the shmem usage of the enclave
> is not properly accounted for, making cgroups ineffective at
> limiting the amount of RAM an enclave can consume.
> 
> For example, when using a cgroup to launch a set of test
> enclaves, the kernel does not properly account for 50% - 75% of
> shmem page allocations on average. In the worst case, when
> nearly all allocations occur during the reclaimer thread, the
> kernel accounts less than a percent of the amount of shmem used
> by the enclave's cgroup to the correct cgroup.
> 
> SGX stores a list of mm_structs that are associated with
> an enclave. Pick one of them during reclaim and charge that
> mm's memcg with the shmem allocation. The one that gets picked
> is arbitrary, but this list almost always only has one mm. The
> cases where there is more than one mm with different memcg's
> are not worth considering.
> 
> Create a new function - sgx_encl_alloc_backing(). This function
> is used whenever a new backing storage page needs to be
> allocated. Previously the same function was used for page
> allocation as well as retrieving a previously allocated page.
> Prior to backing page allocation, if there is a mm_struct associated
> with the enclave that is requesting the allocation, it is set
> as the active memory control group.
> 
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> ---
> V1 -> V2:
>  Changed sgx_encl_set_active_memcg() to simply return the correct
>  memcg for the enclave and renamed to sgx_encl_get_mem_cgroup().
> 
>  Created helper function current_is_ksgxd() to improve readability.
> 
>  Use mmget_not_zero()/mmput_async() when searching mm_list.
> 
>  Move call to set_active_memcg() to sgx_encl_alloc_backing() and
>  use mem_cgroup_put() to avoid leaking a memcg reference.
> 
>  Address review feedback regarding comments and commit log.
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>