linux-kernel - Re: [PATCH V3 0/5] selinux:Significant reduce of preempt

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Message-ID: <1cf240b9-57ee-eee3-228f-5ad4a3a39e57@sony.com>
Date:   Thu, 31 May 2018 11:04:43 +0200
From:   peter enderborg <peter.enderborg@...y.com>
To:     Stephen Smalley <sds@...ho.nsa.gov>,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>,
        James Morris <james.l.morris@...cle.com>,
        Daniel Jurgens <danielj@...lanox.com>,
        Doug Ledford <dledford@...hat.com>, <selinux@...ho.nsa.gov>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH V3 0/5] selinux:Significant reduce of preempt_disable
 holds

On 05/30/2018 10:34 PM, Stephen Smalley wrote:
> On 05/30/2018 10:10 AM, Peter Enderborg wrote:
>> The boolean change becomes a lot more heavy with this patch,
>> but it is a very rare usage in compare with read only operations.
>> The lock held during a policydb_copy is about 1ms on a XEON.
> This has a very substantial performance impact on setsebool, e.g. time setsebool httpd_can_sendmail=1.
> That's because you are doing a full vmalloc();policydb_write();policydb_read();vfree() sequence on it.
> In comparison, KaiGai's old attempt to replace the policy rwlock with RCU only duplicated the conditional policydb state (via a cond_policydb_dup) that he introduced.  Is there a reason you couldn't use that approach?
That one did not make it, so I went for a other path. Make it simple, using the same serialisation that exist. That also make it easier to maintain.
We do not  use the booleans in android since they are not allowed so im not aware of any use case where this administrative function are
used in such frequent manner that it would have an impact. And it must be some other large overhead with interprocess communication and
a multiple writes to sysfs during a boolean settings?  However my concern is/was memory pressure, setting booleans will generate pressure
with lot of atomic allocation and large vmallocs. But my goal is the fast path for real time critical functions such as audio, and it will be a cost for
administrative tasks. On the xeon it takes about ~98 ms to run the security_set_bools compared to about ~8 ms without the overhead
of copying the policydb.  About ~6 ms is rcu sync and ~8 ms is the same as the original update of selinux statuses, and about ~25 ms
is policydb_destroy() of the old copy.
>