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Christopher Obbard a8b49c4bdf um: random: Register random as hwrng-core device 
[ Upstream commit 72d3e093af ]

The UML random driver creates a dummy device under the guest,
/dev/hw_random. When this file is read from the guest, the driver
reads from the host machine's /dev/random, in-turn reading from
the host kernel's entropy pool. This entropy pool could have been
filled by a hardware random number generator or just the host
kernel's internal software entropy generator.

Currently the driver does not fill the guests kernel entropy pool,
this requires a userspace tool running inside the guest (like
rng-tools) to read from the dummy device provided by this driver,
which then would fill the guest's internal entropy pool.

This all seems quite pointless when we are already reading from an
entropy pool, so this patch aims to register the device as a hwrng
device using the hwrng-core framework. This not only improves and
cleans up the driver, but also fills the guest's entropy pool
without having to resort to using extra userspace tools in the guest.

This is typically a nuisance when booting a guest: the random pool
takes a long time (~200s) to build up enough entropy since the dummy
hwrng is not used to fill the guest's pool.

This port was originally attempted by Alexander Neville "dark" (in CC,
discussion in Link), but the conversation there stalled since the
handling of -EAGAIN errors were no removed and longer handled by the
driver. This patch attempts to use the existing method of error
handling but utilises the new hwrng core.

The issue can be noticed when booting a UML guest:

    [    2.560000] random: fast init done
    [  214.000000] random: crng init done

With the patch applied, filling the pool becomes a lot quicker:

    [    2.560000] random: fast init done
    [   12.000000] random: crng init done

Cc: Alexander Neville <dark@volatile.bz>
Link: https://lore.kernel.org/lkml/20190828204609.02a7ff70@TheDarkness/
Link: https://lore.kernel.org/lkml/20190829135001.6a5ff940@TheDarkness.local/
Cc: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Christopher Obbard <chris.obbard@collabora.com>
Acked-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2021-01-06 14:56:55 +01:00
arch um: random: Register random as hwrng-core device 2021-01-06 14:56:55 +01:00
block scsi: block: Fix a race in the runtime power management code 2021-01-06 14:56:50 +01:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: ecdh - avoid unaligned accesses in ecdh_set_secret() 2020-12-30 11:54:10 +01:00
Documentation fbcon: Disable accelerated scrolling 2021-01-06 14:56:51 +01:00
drivers um: random: Register random as hwrng-core device 2021-01-06 14:56:55 +01:00
fs fs/namespace.c: WARN if mnt_count has become negative 2021-01-06 14:56:54 +01:00
include uapi: move constants from <linux/kernel.h> to <linux/const.h> 2021-01-06 14:56:51 +01:00
init initramfs: fix clang build failure 2020-12-11 14:02:14 -08:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel module: delay kobject uevent until after module init call 2021-01-06 14:56:54 +01:00
lib zlib: move EXPORT_SYMBOL() and MODULE_LICENSE() out of dfltcc_syms.c 2021-01-06 14:56:51 +01:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm: memmap defer init doesn't work as expected 2021-01-06 14:56:50 +01:00
net ethtool: fix string set id check 2021-01-06 14:56:48 +01:00
samples samples/bpf: Fix possible hang in xdpsock with multiple threads 2020-12-30 11:53:49 +01:00
scripts kconfig: fix return value of do_error_if() 2020-12-30 11:54:01 +01:00
security ima: Don't modify file descriptor mode on the fly 2020-12-30 11:54:17 +01:00
sound ALSA: rawmidi: Access runtime->avail always in spinlock 2021-01-06 14:56:52 +01:00
tools tools headers UAPI: Sync linux/const.h with the kernel headers 2021-01-06 14:56:51 +01:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt kvm: x86/mmu: Support dirty logging for the TDP MMU 2020-10-23 03:42:13 -04:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-10 15:30:13 -08:00
Makefile Linux 5.10.4 2020-12-30 11:54:29 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.