From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org, patches@lists.linux.dev,
tglx@linutronix.de, linux-crypto@vger.kernel.org,
linux-api@vger.kernel.org, x86@kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>,
Carlos O'Donell <carlos@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
Arnd Bergmann <arnd@arndb.de>, Jann Horn <jannh@google.com>,
Christian Brauner <brauner@kernel.org>,
linux-mm@kvack.org
Subject: Re: [PATCH v14 2/7] mm: add VM_DROPPABLE for designating always lazily freeable mappings
Date: Tue, 3 Jan 2023 21:03:07 +0100 [thread overview]
Message-ID: <Y7SJ+/axonTK0Fir@zx2c4.com> (raw)
In-Reply-To: <CAHk-=whQdWFw+0eGttxsWBHZg1+uh=0MhxXYtvJGX4t9P1MgNw@mail.gmail.com>
Hi Linus,
On Tue, Jan 03, 2023 at 11:54:35AM -0800, Linus Torvalds wrote:
> So 99% of the time, the solution really is just "getrandom()",
> generally with the usual buffering ("read more than you need, so that
> you don't do it all the time").\
That buffering cannot be done safely currently -- VM forks, reseeding
semantics, and so forth. Again, discussed in the cover letter of the
patch if you'd like to engage with those ideas.
> just using your own rng in user space entirely.
This is the thing that isn't quite safe.
> Let me guess: the people you talked to who were excited about this are
> mainly just library people?
No, actually. Mainly people deploying production network-facing things
that need a lot of randomness often. e.g. CBC nonces in TLS, or random
sequence numbers in UDP-based protocols.
> So when you say that this isn't about micro-optimizations, I really
> say "humbug". It's *clearly* about micro-optimization of an area that
> very few people care about, since the alternative is just our existing
> "getrandom()" that is not at all horribly slow.
The alternative is what people currently do, which is attempt to
implement a userspace RNG, which cannot be done safely. Again, -->
cover letter.
> Because the people who actually *use* the random numbers and are *so*
> performance-critical about them already have their own per-thread
> buffers or what-not
...which are not safe.
Anyway, if you're NACK'ing the whole getrandom() vDSO project, just
please outright say so, so I don't spend another 14 revisions in vain.
Jason
next prev parent reply other threads:[~2023-01-03 20:03 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-01 16:29 [PATCH v14 0/7] implement getrandom() in vDSO Jason A. Donenfeld
2023-01-01 16:29 ` [PATCH v14 1/7] x86: lib: Separate instruction decoder MMIO type from MMIO trace Jason A. Donenfeld
2023-01-03 10:32 ` Ingo Molnar
2023-01-03 14:51 ` Jason A. Donenfeld
2023-01-03 17:00 ` Ingo Molnar
2023-01-03 17:29 ` Borislav Petkov
2023-01-03 17:30 ` Jason A. Donenfeld
2023-01-03 17:47 ` Ingo Molnar
2023-01-03 17:48 ` Jason A. Donenfeld
2023-01-04 20:25 ` Ingo Molnar
2023-01-04 20:29 ` Jason A. Donenfeld
2023-01-03 11:00 ` [tip: x86/asm] x86/insn: Avoid namespace clash by separating instruction decoder MMIO type from MMIO trace type tip-bot2 for Jason A. Donenfeld
2023-01-03 17:53 ` [tip: x86/urgent] " tip-bot2 for Jason A. Donenfeld
2023-01-01 16:29 ` [PATCH v14 2/7] mm: add VM_DROPPABLE for designating always lazily freeable mappings Jason A. Donenfeld
2023-01-03 10:50 ` Ingo Molnar
2023-01-03 15:01 ` Jason A. Donenfeld
2023-01-03 18:15 ` Ingo Molnar
2023-01-03 18:51 ` Jason A. Donenfeld
2023-01-03 18:36 ` Andy Lutomirski
2023-01-03 19:05 ` Jason A. Donenfeld
2023-01-03 20:52 ` Andy Lutomirski
2023-01-03 19:19 ` Linus Torvalds
2023-01-03 19:35 ` Jason A. Donenfeld
2023-01-03 19:54 ` Linus Torvalds
2023-01-03 20:03 ` Jason A. Donenfeld [this message]
2023-01-03 20:15 ` Linus Torvalds
2023-01-03 20:25 ` Linus Torvalds
2023-01-03 20:44 ` Jason A. Donenfeld
2023-01-05 21:57 ` Yann Droneaud
2023-01-05 22:57 ` Jason A. Donenfeld
2023-01-06 1:02 ` Linus Torvalds
2023-01-06 2:08 ` Linus Torvalds
2023-01-06 2:42 ` Jason A. Donenfeld
2023-01-06 20:53 ` Andy Lutomirski
2023-01-06 21:10 ` Linus Torvalds
2023-01-10 11:01 ` Dr. Greg
2023-01-06 21:36 ` Jason A. Donenfeld
2023-01-06 21:42 ` Matthew Wilcox
2023-01-06 22:06 ` Linus Torvalds
2023-01-06 2:14 ` Jason A. Donenfeld
2023-01-09 10:34 ` Florian Weimer
2023-01-09 14:28 ` Linus Torvalds
2023-01-11 7:27 ` Eric Biggers
2023-01-11 12:07 ` Linus Torvalds
2023-01-01 16:29 ` [PATCH v14 3/7] x86: mm: Skip faulting instruction for VM_DROPPABLE faults Jason A. Donenfeld
2023-01-01 16:29 ` [PATCH v14 4/7] random: add vgetrandom_alloc() syscall Jason A. Donenfeld
2023-01-01 16:29 ` [PATCH v14 5/7] arch: allocate vgetrandom_alloc() syscall number Jason A. Donenfeld
2023-01-01 16:29 ` [PATCH v14 6/7] random: introduce generic vDSO getrandom() implementation Jason A. Donenfeld
2023-01-01 16:29 ` [PATCH v14 7/7] x86: vdso: Wire up getrandom() vDSO implementation Jason A. Donenfeld
2023-01-12 17:27 ` Christophe Leroy
2023-01-12 17:49 ` Jason A. Donenfeld
2023-01-11 22:23 ` [PATCH v14 0/7] implement getrandom() in vDSO Mathieu Desnoyers
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