Since commit "60253ed1e6ec rng: add request queue support to rng-random",
the use of a spapr_rng device may hang vCPU threads.
The following path is taken without holding the lock to the main loop mutex:
h_random()
rng_backend_request_entropy()
rng_random_request_entropy()
qemu_set_fd_handler()
The consequence is that entropy_available() may be called before the vCPU
thread could even queue the request: depending on the scheduling, it may
happen that entropy_available() does not call random_recv()->qemu_sem_post().
The vCPU thread will then sleep forever in h_random()->qemu_sem_wait().
This could not happen before 60253ed1e6 because entropy_available() used
to call random_recv() unconditionally.
This patch ensures the lock is held to avoid the race.
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Cédric Le Goater <clg@fr.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
It is currently possible to hotplug a spapr_rng device but QEMU crashes
when we try to hot unplug:
ERROR:hw/core/qdev.c:295:qdev_unplug: assertion failed: (hotplug_ctrl)
Aborted
This happens because spapr_rng isn't plugged to any bus and sPAPR does
not provide hotplug support for it: qdev_get_hotplug_handler() hence
return NULL and we hit the assertion.
And anyway, it doesn't make much sense to unplug this device since hcalls
cannot be unregistered. Even the idea of hotplugging a RNG device instead
of declaring it on the QEMU command line looks weird.
This patch simply disables hotpluggability for the spapr-rng class.
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Clean up includes so that osdep.h is included first and headers
which it implies are not included manually.
This commit was created with scripts/clean-includes.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1453832250-766-6-git-send-email-peter.maydell@linaro.org
The PAPR interface defines a hypercall to pass high-quality
hardware generated random numbers to guests. Recent kernels can
already provide this hypercall to the guest if the right hardware
random number generator is available. But in case the user wants
to use another source like EGD, or QEMU is running with an older
kernel, we should also have this call in QEMU, so that guests that
do not support virtio-rng yet can get good random numbers, too.
This patch now adds a new pseudo-device to QEMU that either
directly provides this hypercall to the guest or is able to
enable the in-kernel hypercall if available. The in-kernel
hypercall can be enabled with the use-kvm property, e.g.:
qemu-system-ppc64 -device spapr-rng,use-kvm=true
For handling the hypercall in QEMU instead, a "RngBackend" is
required since the hypercall should provide "good" random data
instead of pseudo-random (like from a "simple" library function
like rand() or g_random_int()). Since there are multiple RngBackends
available, the user must select an appropriate back-end via the
"rng" property of the device, e.g.:
qemu-system-ppc64 -object rng-random,filename=/dev/hwrng,id=gid0 \
-device spapr-rng,rng=gid0 ...
See http://wiki.qemu-project.org/Features-Done/VirtIORNG for
other example of specifying RngBackends.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Greg Kurz