linux-kernel - Re: [PATCH v1] random: block in /dev/urandom

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Date:   Mon, 25 Apr 2022 13:09:34 +0100
From:   Mark Brown <broonie@...nel.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Guenter Roeck <linux@...ck-us.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Nick Hu <nickhu@...estech.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        "David S . Miller" <davem@...emloft.net>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Michal Simek <monstr@...str.eu>,
        Borislav Petkov <bp@...en8.de>, Guo Ren <guoren@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Joshua Kinard <kumba@...too.org>,
        David Laight <David.Laight@...lab.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Eric Biggers <ebiggers@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Lennart Poettering <mzxreary@...inter.de>,
        Konstantin Ryabitsev <konstantin@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH v1] random: block in /dev/urandom

On Sat, Apr 23, 2022 at 02:52:51AM +0200, Jason A. Donenfeld wrote:
> On Wed, Mar 23, 2022 at 4:53 PM Arnd Bergmann <arnd@...db.de> wrote:

> > Maybe kernelci has a virtio-rng device assigned to the machine
> > and you don't? That would clearly avoid the issue here.

> Indeed it's probably something like that. Or maybe they're networked
> with something that has a steady stream of interrupts. I say this
> because I was able to reproduce Guenter's findings using the
> versatilepb machine with the versatile_defconfig config and the
> versatile-pb.dtb file. Indeed this board doesn't have a cycle counter.
> However, I did have success using the fallback timer and the other
> patches in the jd/for-guenter branch, so at least for versatile's
> nuances, I think (hope?) there's a reasonable success story here.

There's no virtio-rng device being instantiated, unless qemu is doing
that by default (I can't see anything in the logs that suggests it did).
There is networking though.  A sample command for invoking qemu for
versatilepb is:

qemu-system-arm -cpu arm926 -machine versatilepb -nographic -net nic,model=smc91c111,macaddr=52:54:00:12:34:58 -net user -m 256 -monitor none -dtb /var/lib/lava/dispatcher/tmp/85180/deployimages-hitd6sn_/dtb/versatile-pb.dtb -kernel /var/lib/lava/dispatcher/tmp/85180/deployimages-hitd6sn_/kernel/zImage -append "console=ttyAMA0,115200 root=/dev/ram0 debug verbose console_msg_format=syslog earlycon" -initrd /var/lib/lava/dispatcher/tmp/85180/deployimages-hitd6sn_/ramdisk/rootfs.cpio.gz -drive format=qcow2,file=/var/lib/lava/dispatcher/tmp/85180/apply-overlay-guest-l9_f_lxl/lava-guest.qcow2,media=disk,if=scsi,id=lavatest

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