From: Pavel Machek <pavel@ucw.cz>
To: Michal Hocko <mhocko@kernel.org>
Cc: Jann Horn <jannh@google.com>,
"Catangiu, Adrian Costin" <acatan@amazon.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
"virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"rjw@rjwysocki.net" <rjw@rjwysocki.net>,
"len.brown@intel.com" <len.brown@intel.com>,
"fweimer@redhat.com" <fweimer@redhat.com>,
"keescook@chromium.org" <keescook@chromium.org>,
"luto@amacapital.net" <luto@amacapital.net>,
"wad@chromium.org" <wad@chromium.org>,
"mingo@kernel.org" <mingo@kernel.org>,
"bonzini@gnu.org" <bonzini@gnu.org>, "Graf (AWS),
Alexander" <graf@amazon.de>,
"MacCarthaigh, Colm" <colmmacc@amazon.com>,
"Singh, Balbir" <sblbir@amazon.com>,
"Sandu, Andrei" <sandreim@amazon.com>,
"Brooker, Marc" <mbrooker@amazon.com>,
"Weiss, Radu" <raduweis@amazon.com>,
"Manwaring, Derek" <derekmn@amazon.com>
Subject: Re: [RFC]: mm,power: introduce MADV_WIPEONSUSPEND
Date: Tue, 7 Jul 2020 18:37:58 +0200 [thread overview]
Message-ID: <20200707163758.GA1947@amd> (raw)
In-Reply-To: <20200707085847.GA5913@dhcp22.suse.cz>
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Hi!
> > > > You can do it seqlock-style, kind of - you reserve the first byte of
> > > > the page or so as a "is this page initialized" marker, and after every
> > > > read from the page, you do a compiler barrier and check whether that
> > > > byte has been cleared.
> > >
> > > This is certainly possible yet wery awkwar interface to use IMHO.
> > > MADV_EXTERNALY_VOLATILE would express the actual semantic much better.
> > > I might not still understand the expected usecase but if the target
> > > application has to be changed anyway then why not simply use a
> > > transparent and proper signaling mechanism like poll on a fd. That
> >
> > The goal is to have cryprographically-safe get_random_number() with 0
> > syscalls.
> >
> > You'd need to do:
> >
> > if (!poll(did_i_migrate)) {
> > use_prng_seed();
> > if (poll(did_i_migrate)) {
> > /* oops_they_migrated_me_in_middle_of_computation,
> > lets_redo_it() */
> > goto retry:
> > }
> > }
> >
> > Which means two syscalls..
>
> Is this a real problem though? Do we have any actual numbers? E.g. how
> often does the migration happen so that 2 syscalls would be visible in
> actual workloads?
Please go through the thread and try to understand it.
You'd need syscalls per get_randomness(), not per migration.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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next prev parent reply other threads:[~2020-07-07 16:38 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-03 10:34 [RFC]: mm,power: introduce MADV_WIPEONSUSPEND Catangiu, Adrian Costin
2020-07-03 11:04 ` Jann Horn
2020-07-04 1:33 ` Colm MacCárthaigh
2020-07-06 12:09 ` Alexander Graf
2020-07-03 11:30 ` Michal Hocko
2020-07-03 12:17 ` Rafael J. Wysocki
2020-07-03 22:39 ` Pavel Machek
2020-07-03 13:29 ` Jann Horn
2020-07-03 22:34 ` Pavel Machek
2020-07-03 22:53 ` Jann Horn
2020-07-07 7:38 ` Michal Hocko
2020-07-07 8:07 ` Pavel Machek
2020-07-07 8:58 ` Michal Hocko
2020-07-07 16:37 ` Pavel Machek [this message]
[not found] ` <E6B41570-E206-4458-921B-465B9EF74949@amazon.com>
2020-07-12 7:22 ` Pavel Machek
2020-07-13 8:02 ` Michal Hocko
2020-07-04 1:45 ` Colm MacCárthaigh
2020-07-07 7:40 ` Michal Hocko
2020-07-03 22:44 ` Pavel Machek
2020-07-03 22:56 ` Jann Horn
2020-07-04 11:48 ` Pavel Machek
2020-07-06 12:26 ` Alexander Graf
2020-07-06 12:52 ` Jann Horn
2020-07-06 13:14 ` Alexander Graf
2020-07-07 7:44 ` Michal Hocko
2020-07-07 8:01 ` Alexander Graf
2020-07-07 9:14 ` Michal Hocko
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