Message-ID: <5844ee9f-1992-a62a-2141-3b694a1e1915@redhat.com>
Date:   Tue, 24 Jan 2023 17:38:39 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Stefan Roesch <shr@...kernel.io>, linux-mm@...ck.org
Cc:     linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, CGEL <cgel.zte@...il.com>,
        Michal Hocko <mhocko@...nel.org>, Jann Horn <jannh@...gle.com>
Subject: Re: [RESEND RFC PATCH v1 00/20] mm: process/cgroup ksm support

On 23.01.23 18:37, Stefan Roesch wrote:
> So far KSM can only be enabled by calling madvise for memory regions. What is
> required to enable KSM for more workloads is to enable / disable it at the
> process / cgroup level.

Did you stumble over the proposals from last year to enable this 
per-process [1] and system-wide [2]? I remember there was also regarding 
enabling it system-wide.

I'm going to point out the security aspect, and that e.g., Windows used 
to enable it system-wide before getting taught by security experts 
otherwise. Details on KSM and security aspects can be found in that thread.

Long story short: one has to be very careful with that and only enable 
it for very carefully selected worklads. Letting a workload opt-in on a 
VMA level is most probably safer than an admin blindly turning this on 
for random processes ...

Last attempts got nacked ...

[1] 
https://lore.kernel.org/all/20220517092701.1662641-1-xu.xin16@zte.com.cn/
[2] https://lore.kernel.org/all/20220609055658.703472-1-xu.xin16@zte.com.cn/

> 
> 1. New options for prctl system command
> This patch series adds two new options to the prctl system call. The first
> one allows to enable KSM at the process level and the second one to query the
> setting.
> 
> The setting will be inherited by child processes.
> 
> With the above setting, KSM can be enabled for the seed process of a cgroup
> and all processes in the cgroup will inherit the setting.
> 
> 2. Changes to KSM processing
> When KSM is enabled at the process level, the KSM code will iterate over all
> the VMA's and enable KSM for the eligible VMA's.
> 
> When forking a process that has KSM enabled, the setting will be inherited by
> the new child process.
> 
> In addition when KSM is disabled for a process, KSM will be disabled for the
> VMA's where KSM has been enabled.
> 
> 3. Add tracepoints to KSM
> Currently KSM has no tracepoints. This adds tracepoints to the key KSM functions
> to make it easier to debug KSM.
> 
> 4. Add general_profit metric
> The general_profit metric of KSM is specified in the documentation, but not
> calculated. This adds the general profit metric to /sys/kernel/debug/mm/ksm.
> 
> 5. Add more metrics to ksm_stat
> This adds the process profit and ksm type metric to /proc/<pid>/ksm_stat.
> 
> 6. Add more tests to ksm_tests
> This adds an option to specify the merge type to the ksm_tests. This allows to
> test madvise and prctl KSM. It also adds a new option to query if prctl KSM has
> been enabled. It adds a fork test to verify that the KSM process setting is
> inherited by client processes.
> 
> 
> Stefan Roesch (20):
>    mm: add new flag to enable ksm per process
>    mm: add flag to __ksm_enter
>    mm: add flag to __ksm_exit call
>    mm: invoke madvise for all vmas in scan_get_next_rmap_item
>    mm: support disabling of ksm for a process
>    mm: add new prctl option to get and set ksm for a process
>    mm: add tracepoints to ksm
>    mm: split off pages_volatile function
>    mm: expose general_profit metric
>    docs: document general_profit sysfs knob
>    mm: calculate ksm process profit metric
>    mm: add ksm_merge_type() function
>    mm: expose ksm process profit metric in ksm_stat
>    mm: expose ksm merge type in ksm_stat
>    docs: document new procfs ksm knobs
>    tools: add new prctl flags to prctl in tools dir
>    selftests/vm: add KSM prctl merge test
>    selftests/vm: add KSM get merge type test
>    selftests/vm: add KSM fork test
>    selftests/vm: add two functions for debugging merge outcome
> 
>   Documentation/ABI/testing/sysfs-kernel-mm-ksm |   8 +
>   Documentation/admin-guide/mm/ksm.rst          |   8 +-
>   MAINTAINERS                                   |   1 +
>   fs/proc/base.c                                |   5 +
>   include/linux/ksm.h                           |  19 +-
>   include/linux/sched/coredump.h                |   1 +
>   include/trace/events/ksm.h                    | 257 ++++++++++++++++++
>   include/uapi/linux/prctl.h                    |   2 +
>   kernel/sys.c                                  |  29 ++
>   mm/ksm.c                                      | 134 ++++++++-
>   tools/include/uapi/linux/prctl.h              |   2 +
>   tools/testing/selftests/vm/Makefile           |   3 +-
>   tools/testing/selftests/vm/ksm_tests.c        | 254 ++++++++++++++---
>   13 files changed, 665 insertions(+), 58 deletions(-)
>   create mode 100644 include/trace/events/ksm.h
> 
> 
> base-commit: c1649ec55708ae42091a2f1bca1ab49ecd722d55

-- 
Thanks,

David / dhildenb

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