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[5.69.146.176]) by smtp.gmail.com with ESMTPSA id k14-20020a5d66ce000000b002f103ca90cdsm15992195wrw.101.2023.04.19.06.53.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Apr 2023 06:53:11 -0700 (PDT) Date: Wed, 19 Apr 2023 14:53:13 +0100 From: Jean-Philippe Brucker To: Andre Przywara Cc: Will Deacon , Julien Thierry , kvm@vger.kernel.org, Alexandru Elisei , Sami Mujawar Subject: Re: [PATCH kvmtool 1/2] virtio/rng: switch to using /dev/urandom Message-ID: <20230419135313.GA94027@myrica> References: <20230413165757.1728800-1-andre.przywara@arm.com> <20230413165757.1728800-2-andre.przywara@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230413165757.1728800-2-andre.przywara@arm.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Apr 13, 2023 at 05:57:56PM +0100, Andre Przywara wrote: > At the moment we use /dev/random as the backing device to provide random > numbers to our virtio-rng implementation. The downside of doing so is > that it may block indefinitely - or return EAGAIN repeatedly in our case. > On one headless systbem without ample noise sources (no keyboard, mouse, system > or network traffic) I measured 30 seconds to gain one byte of randomness. > At the moment EDK II insists in waiting for all of the requsted random > bytes (for its EFI_RNG_PROTOCOL runtime service) to arrive, that held up > a Linux kernel boot for more than 10 minutes(!). > > According to the Internet(TM), on Linux /dev/urandom provides the same > quality random numbers as /dev/random, it just does not block when the > entropy estimation algorithm suggests so. For all practical purposes the > recommendation is to just use /dev/urandom, QEMU did the switch as well > in 2019 [1]. > > Use /dev/urandom instead of /dev/random when opening the file descriptor > providing the randomness source for the virtio/rng implementation. > > [1] https://gitlab.com/qemu-project/qemu/-/commit/a2230bd778d8 > > Signed-off-by: Andre Przywara Reviewed-by: Jean-Philippe Brucker > --- > virtio/rng.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/virtio/rng.c b/virtio/rng.c > index 8f85d5ec1..eab8f3ac0 100644 > --- a/virtio/rng.c > +++ b/virtio/rng.c > @@ -166,7 +166,7 @@ int virtio_rng__init(struct kvm *kvm) > if (rdev == NULL) > return -ENOMEM; > > - rdev->fd = open("/dev/random", O_RDONLY | O_NONBLOCK); > + rdev->fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK); > if (rdev->fd < 0) { > r = rdev->fd; > goto cleanup; > -- > 2.25.1 >