Commit fd8aa9095a ("xen: optimize xenbus driver for multiple concurrent
xenstore accesses") optimized xenbus concurrent accesses but in doing so
broke UABI of /dev/xen/xenbus. Through /dev/xen/xenbus applications are in
charge of xenbus message exchange with the correct header and body. Now,
after the mentioned commit the replies received by application will no
longer have the header req_id echoed back as it was on request (see
specification below for reference), because that particular field is being
overwritten by kernel.
struct xsd_sockmsg
{
uint32_t type; /* XS_??? */
uint32_t req_id;/* Request identifier, echoed in daemon's response. */
uint32_t tx_id; /* Transaction id (0 if not related to a transaction). */
uint32_t len; /* Length of data following this. */
/* Generally followed by nul-terminated string(s). */
};
Before there was only one request at a time so req_id could simply be
forwarded back and forth. To allow simultaneous requests we need a
different req_id for each message thus kernel keeps a monotonic increasing
counter for this field and is written on every request irrespective of
userspace value.
Forwarding again the req_id on userspace requests is not a solution because
we would open the possibility of userspace-generated req_id colliding with
kernel ones. So this patch instead takes another route which is to
artificially keep user req_id while keeping the xenbus logic as is. We do
that by saving the original req_id before xs_send(), use the private kernel
counter as req_id and then once reply comes and was validated, we restore
back the original req_id.
Cc: <stable@vger.kernel.org> # 4.11
Fixes: fd8aa9095a ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
Reported-by: Bhavesh Davda <bhavesh.davda@oracle.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Handling of multiple concurrent Xenstore accesses through xenbus driver
either from the kernel or user land is rather lame today: xenbus is
capable to have one access active only at one point of time.
Rewrite xenbus to handle multiple requests concurrently by making use
of the request id of the Xenstore protocol. This requires to:
- Instead of blocking inside xb_read() when trying to read data from
the xenstore ring buffer do so only in the main loop of
xenbus_thread().
- Instead of doing writes to the xenstore ring buffer in the context of
the caller just queue the request and do the write in the dedicated
xenbus thread.
- Instead of just forwarding the request id specified by the caller of
xenbus to xenstore use a xenbus internal unique request id. This will
allow multiple outstanding requests.
- Modify the locking scheme in order to allow multiple requests being
active in parallel.
- Instead of waiting for the reply of a user's xenstore request after
writing the request to the xenstore ring buffer return directly to
the caller and do the waiting in the read path.
Additionally signal handling was optimized by avoiding waking up the
xenbus thread or sending an event to Xenstore in case the addressed
entity is known to be running already.
As a result communication with Xenstore is sped up by a factor of up
to 5: depending on the request type (read or write) and the amount of
data transferred the gain was at least 20% (small reads) and went up to
a factor of 5 for large writes.
In the end some more rough edges of xenbus have been smoothed:
- Handling of memory shortage when reading from xenstore ring buffer in
the xenbus driver was not optimal: it was busy looping and issuing a
warning in each loop.
- In case of xenstore not running in dom0 but in a stubdom we end up
with two xenbus threads running as the initialization of xenbus in
dom0 expecting a local xenstored will be redone later when connecting
to the xenstore domain. Up to now this was no problem as locking
would prevent the two xenbus threads interfering with each other, but
this was just a waste of kernel resources.
- An out of memory situation while writing to or reading from the
xenstore ring buffer no longer will lead to a possible loss of
synchronization with xenstore.
- The user read and write part are now interruptible by signals.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
The xenbus driver has an awful mixture of internally and globally
visible headers: some of the internally used only stuff is defined in
the global header include/xen/xenbus.h while some stuff defined in
internal headers is used by other drivers, too.
Clean this up by moving the externally used symbols to
include/xen/xenbus.h and the symbols used internally only to a new
header drivers/xen/xenbus/xenbus.h replacing xenbus_comms.h and
xenbus_probe.h
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
drivers/xen/xenbus/xenbus_comms.c uses
full memory barriers to communicate with the other side.
For guests compiled with CONFIG_SMP, smp_wmb and smp_mb
would be sufficient, so mb() and wmb() here are only needed if
a non-SMP guest runs on an SMP host.
Switch to virt_xxx barriers which serve this exact purpose.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Convert printks to pr_<level> (excludes printk(KERN_DEBUG...)
to be more consistent throughout the xen subsystem.
Add pr_fmt with KBUILD_MODNAME or "xen:" KBUILD_MODNAME
Coalesce formats and add missing word spaces
Add missing newlines
Align arguments and reflow to 80 columns
Remove DRV_NAME from formats as pr_fmt adds the same content
This does change some of the prefixes of these messages
but it also does make them more consistent.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
bind_evtchn_to_irqhandler can legitimately return 0 (irq 0): it is not
an error.
If Linux is running as an HVM domain and is running as Dom0, use
xenstored_local_init to initialize the xenstore page and event channel.
Changes in v4:
- do not xs_reset_watches on dom0.
Changes in v2:
- refactor xenbus_init.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
[v5: Fixed case switch indentations]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Add an ioctl to the /dev/xen/xenbus_backend device allowing the xenbus
backend to be started after the kernel has booted. This allows xenstore
to run in a different domain from the dom0.
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
After triggering a crash dump in a HVM guest, the PV backend drivers
will remain in Connected state. When the kdump kernel starts the PV
drivers will skip such devices. As a result, no root device is found and
the vmcore cant be saved.
A similar situation happens after a kexec boot, here the devices will be
in the Closed state.
With this change all frontend devices with state XenbusStateConnected or
XenbusStateClosed will be reset by changing the state file to Closing ->
Closed -> Initializing. This will trigger a disconnect in the backend
drivers. Now the frontend drivers will find the backend drivers in state
Initwait and can connect.
Signed-off-by: Olaf Hering <olaf@aepfle.de>
[v2:
- add timeout when waiting for backend state change
(based on feedback from Ian Campell)
- extent printk message to include backend string
- add comment to fall-through case in xenbus_reset_frontend]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
When restoring, rebind the existing xenbus irq to the new xenbus event
channel. (It turns out in practice that this is always the same, and
is never updated on restore. That's a bug, but Xeno-linux has been
like this for a long time, so it can't really be fixed.)
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This communicates with the machine control software via a registry
residing in a controlling virtual machine. This allows dynamic
creation, destruction and modification of virtual device
configurations (network devices, block devices and CPUS, to name some
examples).
[ Greg, would you mind giving this a review? Thanks -J ]
Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Greg KH <greg@kroah.com>
