linux-kernel - Re: BUG selftests/mm]

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Date: Mon, 11 Mar 2024 15:28:26 -0400
From: Peter Xu <peterx@...hat.com>
To: Axel Rasmussen <axelrasmussen@...gle.com>
Cc: David Hildenbrand <david@...hat.com>,
	Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: BUG selftests/mm]

On Mon, Mar 11, 2024 at 11:59:59AM -0700, Axel Rasmussen wrote:
> I'd prefer not to require root or CAP_SYS_ADMIN or similar for
> UFFDIO_POISON, because those control access to lots more things
> besides, which we don't necessarily want the process using UFFD to be
> able to do. :/
> 
> Ratelimiting seems fairly reasonable to me. I do see the concern about
> dropping some addresses though.

Do you know how much could an admin rely on such addresses?  How frequent
would MCE generate normally in a sane system?

> Perhaps we can mitigate that concern by defining our own ratelimit
> interval/burst configuration?

Any details?

> Another idea would be to only ratelimit it if !CONFIG_DEBUG_VM or
> similar. Not sure if that's considered valid or not. :)

This, OTOH, sounds like an overkill..

I just checked again on the detail of ratelimit code, where we by default
it has:

#define DEFAULT_RATELIMIT_INTERVAL	(5 * HZ)
#define DEFAULT_RATELIMIT_BURST		10

So it allows a 10 times burst rather than 2.. IIUC it means even if
there're continous 10 MCEs it won't get suppressed, until the 11th came, in
5 seconds interval.  I think it means it's possibly even less of a concern
to directly use pr_err_ratelimited().

Thanks,

-- 
Peter Xu