From: Aurelien Jarno <aurelien@aurel32.net>
To: kvm@vger.kernel.org
Cc: Ian Molton <ian.molton@collabora.co.uk>,
Matt Mackall <mpm@selenic.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Herbert Xu <herbert@gondor.apana.org.au>
Subject: virtio-rng only returns zeros with CONFIG_HW_RANDOM=m
Date: Mon, 25 Feb 2013 00:11:54 +0100 [thread overview]
Message-ID: <20130224231154.GA30477@hall.aurel32.net> (raw)
Hi,
I have noticed that virtio-rng only returns zero for kernels >= 2.6.33
built with CONFIG_HW_RANDOM=m. This is a bit much too predictable for a
random generator ;-).
The reason for that is virtio expects guest real addresses, while
rng_core.ko (ie when built as a module) is passing a vmalloced buffer
to the virtio-rng read function, declared as such:
static u8 rng_buffer[SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES]
__cacheline_aligned;
This is basically the same issue than the following one:
https://lists.linux-foundation.org/pipermail/virtualization/2008-May/010946.html
but introduced in a more subtle way in this commit:
commit bb347d98079a547e80bd4722dee1de61e4dca0e8
Author: Ian Molton <ian.molton@collabora.co.uk>
Date: Tue Dec 1 15:26:33 2009 +0800
hwrng: virtio-rng - Convert to new API
This patch converts virtio-rng to the new hw_rng API.
In the process it fixes a previously untriggered buffering bug where the
buffer is not drained correctly if it has a non-multiple-of-4 length.
Performance has improved under qemu-kvm testing also.
Signed-off-by: Ian Molton <ian.molton@collabora.co.uk>
Acked-by: Matt Mackall <mpm@selenic.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
I basically see three possible way of fixing that:
- prevent rng_core to be built as a module;
- use an intermediary kmalloced buffer in virtio-rng passed to virtio
functions, followed by a memcpy to get the data in the rng core
buffer;
- use a kmalloc buffer in rng_core instead of vmalloc one.
What would be best way to fix that? Did I miss another way?
Thanks,
Aurelien
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurelien@aurel32.net http://www.aurel32.net
next reply other threads:[~2013-02-24 23:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-24 23:11 Aurelien Jarno [this message]
2013-02-27 0:13 ` virtio-rng only returns zeros with CONFIG_HW_RANDOM=m Rusty Russell
2013-02-27 3:40 ` Ben Hutchings
2013-02-27 10:33 ` Aurelien Jarno
2013-02-27 13:22 ` Jens Axboe
2013-02-28 3:00 ` Rusty Russell
2013-05-30 1:07 ` Rusty Russell
2013-05-30 7:18 ` Jens Axboe
2013-02-27 1:26 ` Rusty Russell
2013-02-27 16:36 ` Aurelien Jarno
2013-02-28 3:04 ` Rusty Russell
2013-03-10 8:26 ` Herbert Xu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20130224231154.GA30477@hall.aurel32.net \
--to=aurelien@aurel32.net \
--cc=herbert@gondor.apana.org.au \
--cc=ian.molton@collabora.co.uk \
--cc=kvm@vger.kernel.org \
--cc=mpm@selenic.com \
--cc=rusty@rustcorp.com.au \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.