linux-hardening - Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the vmalloc check.

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Message-ID: <Z08Gz51WO8QFyVFo@pc636>
Date: Tue, 3 Dec 2024 14:25:35 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: zuoze <zuoze1@...wei.com>
Cc: Uladzislau Rezki <urezki@...il.com>,
	Matthew Wilcox <willy@...radead.org>, gustavoars@...nel.org,
	akpm@...ux-foundation.org, linux-hardening@...r.kernel.org,
	linux-mm@...ck.org, keescook@...omium.org,
	wangkefeng.wang@...wei.com
Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass
 the vmalloc check.

> > On Tue, Dec 03, 2024 at 07:23:44PM +0800, zuoze wrote:
> > > We have implemented host-guest communication based on the TUN device
> > > using XSK[1]. The hardware is a Kunpeng 920 machine (ARM architecture),
> > > and the operating system is based on the 6.6 LTS version with kernel
> > > version 6.6. The specific stack for hotspot collection is as follows:
> > > 
> > > -  100.00%     0.00%  vhost-12384  [unknown]      [k] 0000000000000000
> > >     - ret_from_fork
> > >        - 99.99% vhost_task_fn
> > >           - 99.98% 0xffffdc59f619876c
> > >              - 98.99% handle_rx_kick
> > >                 - 98.94% handle_rx
> > >                    - 94.92% tun_recvmsg
> > >                       - 94.76% tun_do_read
> > >                          - 94.62% tun_put_user_xdp_zc
> > >                             - 63.53% __check_object_size
> > >                                - 63.49% __check_object_size.part.0
> > >                                     find_vmap_area
> > >                             - 30.02% _copy_to_iter
> > >                                  __arch_copy_to_user
> > >                    - 2.27% get_rx_bufs
> > >                       - 2.12% vhost_get_vq_desc
> > >                            1.49% __arch_copy_from_user
> > >                    - 0.89% peek_head_len
> > >                         0.54% xsk_tx_peek_desc
> > >                    - 0.68% vhost_add_used_and_signal_n
> > >                       - 0.53% eventfd_signal
> > >                            eventfd_signal_mask
> > >              - 0.94% handle_tx_kick
> > >                 - 0.94% handle_tx
> > >                    - handle_tx_copy
> > >                       - 0.59% vhost_tx_batch.constprop.0
> > >                            0.52% tun_sendmsg
> > > 
> > > It can be observed that most of the overhead is concentrated in the
> > > find_vmap_area function.
> > > 
> > I see. Yes, it is pretty contented, since you run the v6.6 kernel. There
> > was a work that tends to improve it to mitigate a vmap lock contention.
> > See it here: https://lwn.net/Articles/956590/
> > 
> > The work was taken in the v6.9 kernel:
> > 
> > <snip>
> > commit 38f6b9af04c4b79f81b3c2a0f76d1de94b78d7bc
> > Author: Uladzislau Rezki (Sony) <urezki@...il.com>
> > Date:   Tue Jan 2 19:46:23 2024 +0100
> > 
> >      mm: vmalloc: add va_alloc() helper
> > 
> >      Patch series "Mitigate a vmap lock contention", v3.
> > 
> >      1. Motivation
> > ...
> > <snip>
> > 
> > Could you please try the v6.9 kernel on your setup?
> > 
> > How to solve it, probably, it can be back-ported to the v6.6 kernel.
> 
> All the vmalloc-related optimizations have already been merged into 6.6,
> including the set of optimization patches you suggested. Thank you very
> much for your input.
> 
Do you mean that the perf-data that you posted to this email thread,
contains the: Patch series "Mitigate a vmap lock contention", v3. from the v6.9?

and you still see a high contention?

Thank you!

--
Uladzislau Rezki