Re: [PATCH v4 2/2] xen/console: add compile-time rate-limiting controls

On Mon, Aug 10, 2026 at 03:06:35PM +0200, Roger Pau Monné wrote:
> On Wed, Jul 29, 2026 at 12:25:20AM -0700, [email protected] wrote:
> > From: Denis Mukhin <[email protected]> 
> > 
> > Introduce CONFIG_PRINTK_RATELIMIT_MS and CONFIG_PRINTK_RATELIMIT_BURST
> > for configuring rate-limiting policy at the compile time.
> > 
> > Use symbols for global rate-limiting initialization in the console driver.
> > 
> > Signed-off-by: Denis Mukhin <[email protected]>
> > ---
> > Changes since v3:
> > - added note on security support for non-standard configurations
> > - gated menu with EXPERT
> > 
> > I kept both settings for now.
> > ---
> >  xen/common/Kconfig         | 36 ++++++++++++++++++++++++++++++++++++
> >  xen/drivers/char/console.c |  6 ++++--
> >  2 files changed, 40 insertions(+), 2 deletions(-)
> > 
> > diff --git a/xen/common/Kconfig b/xen/common/Kconfig
> > index da80fdba8469..749d3bfb08e0 100644
> > --- a/xen/common/Kconfig
> > +++ b/xen/common/Kconfig
> > @@ -672,4 +672,40 @@ config PM_STATS
> >  	  Enable collection of performance management statistics to aid in
> >  	  analyzing and tuning power/performance characteristics of the system
> >  
> > +menu "Console rate-limiting"
> > +	visible if EXPERT
> 
> No strong opinion, but there's a drivers/char/Kconfig which might be a
> more natural place for those option to live, and then there's no
> reason for the extra menu?

I had the knob initially in drivers/char/Kconfig, but moved to
common/Kconfig to address Jan's feedback:

  https://lore.kernel.org/xen-devel/[email protected]/

> 
> > +
> > +config PRINTK_RATELIMIT_MS
> > +	int "printk rate-limiting time window (milliseconds)"
> > +	default 5000
> > +	help
> > +	  Specifies the time window, in milliseconds, for rate-limited [*] printk
> > +	  messages. No more than `CONFIG_PRINTK_RATELIMIT_BURST` messages will be
> > +	  printed within this window.
> > +
> > +	  Setting this value to 0 disables rate-limiting entirely.
> > +
> > +	  Configurations using a value other than the default of 5000 are not
> > +	  security supported.
> > +
> > +	  [*] Rate-limited messages are those controlled by the `loglvl` and
> > +	  `guest_loglvl` command-line parameters.
> > +
> > +config PRINTK_RATELIMIT_BURST
> > +	int "printk rate-limited message burst size"
> > +	default 10
> > +	help
> > +	  Defines the maximum number of rate-limited [*] printk messages that may
> > +	  be printed within each `CONFIG_PRINTK_RATELIMIT_MS` time window.
> > +
> > +	  Setting this value to 0 disables rate-limiting entirely.
> > +
> > +	  Configurations using a value other than the default of 10 are not
> > +	  security supported.
> > +
> > +	  [*] Rate-limited messages are those controlled by the `loglvl` and
> > +	  `guest_loglvl` command-line parameters.
> 
> Is it common to use footnotes in Kconfig options?  It seems a bit
> weird to me, I would probably just expand inside parenthesis if
> needed.

I'll just drop extra text.

> 
> Also, I'm a bit confused by the mention of loglvl and guest_loglvl
> explicitly here: messages outside of the selected level are just
> discarded, and hence it's kind of obvious that just messages inside
> the selected level are controlled by this rate-limiting.