On Fri, Mar 25, 2022 at 6:10 PM Michael S. Tsirkin <mst at redhat.com>
wrote:>
> On Fri, Mar 25, 2022 at 05:20:19PM +0800, Jason Wang wrote:
> > On Fri, Mar 25, 2022 at 5:10 PM Michael S. Tsirkin <mst at
redhat.com> wrote:
> > >
> > > On Fri, Mar 25, 2022 at 03:52:00PM +0800, Jason Wang wrote:
> > > > On Fri, Mar 25, 2022 at 2:31 PM Michael S. Tsirkin <mst
at redhat.com> wrote:
> > > > >
> > > > > Bcc:
> > > > > Subject: Re: [PATCH 3/3] virtio: harden vring IRQ
> > > > > Message-ID: <20220325021422-mutt-send-email-mst at
kernel.org>
> > > > > Reply-To:
> > > > > In-Reply-To: <f7046303-7d7d-e39f-3c71-3688126cc812
at redhat.com>
> > > > >
> > > > > On Fri, Mar 25, 2022 at 11:04:08AM +0800, Jason Wang
wrote:
> > > > > >
> > > > > > ? 2022/3/24 ??7:03, Michael S. Tsirkin ??:
> > > > > > > On Thu, Mar 24, 2022 at 04:40:04PM +0800,
Jason Wang wrote:
> > > > > > > > This is a rework on the previous IRQ
hardening that is done for
> > > > > > > > virtio-pci where several drawbacks were
found and were reverted:
> > > > > > > >
> > > > > > > > 1) try to use IRQF_NO_AUTOEN which is
not friendly to affinity managed IRQ
> > > > > > > > that is used by some device such as
virtio-blk
> > > > > > > > 2) done only for PCI transport
> > > > > > > >
> > > > > > > > In this patch, we tries to borrow the
idea from the INTX IRQ hardening
> > > > > > > > in the reverted commit 080cd7c3ac87
("virtio-pci: harden INTX interrupts")
> > > > > > > > by introducing a global irq_soft_enabled
variable for each
> > > > > > > > virtio_device. Then we can to toggle it
during
> > > > > > > >
virtio_reset_device()/virtio_device_ready(). A synchornize_rcu() is
> > > > > > > > used in virtio_reset_device() to
synchronize with the IRQ handlers. In
> > > > > > > > the future, we may provide config_ops
for the transport that doesn't
> > > > > > > > use IRQ. With this, vring_interrupt()
can return check and early if
> > > > > > > > irq_soft_enabled is false. This lead to
smp_load_acquire() to be used
> > > > > > > > but the cost should be acceptable.
> > > > > > > Maybe it should be but is it? Can't we
use synchronize_irq instead?
> > > > > >
> > > > > >
> > > > > > Even if we allow the transport driver to
synchornize through
> > > > > > synchronize_irq() we still need a check in the
vring_interrupt().
> > > > > >
> > > > > > We do something like the following previously:
> > > > > >
> > > > > > if
(!READ_ONCE(vp_dev->intx_soft_enabled))
> > > > > > return IRQ_NONE;
> > > > > >
> > > > > > But it looks like a bug since speculative read can
be done before the check
> > > > > > where the interrupt handler can't see the
uncommitted setup which is done by
> > > > > > the driver.
> > > > >
> > > > > I don't think so - if you sync after setting the
value then
> > > > > you are guaranteed that any handler running afterwards
> > > > > will see the new value.
> > > >
> > > > The problem is not disabled but the enable.
> > >
> > > So a misbehaving device can lose interrupts? That's not a
problem at all
> > > imo.
> >
> > It's the interrupt raised before setting irq_soft_enabled to true:
> >
> > CPU 0 probe) driver specific setup (not commited)
> > CPU 1 IRQ handler) read the uninitialized variable
> > CPU 0 probe) set irq_soft_enabled to true
> > CPU 1 IRQ handler) read irq_soft_enable as true
> > CPU 1 IRQ handler) use the uninitialized variable
> >
> > Thanks
>
> Yea, it hurts if you do it. So do not do it then ;).
>
> irq_soft_enabled (I think driver_ok or status is a better name)
I can change it to driver_ok.
> should be initialized to false *before* irq is requested.
>
> And requesting irq commits all memory otherwise all drivers would be
> broken,
So I think we might talk different issues:
1) Whether request_irq() commits the previous setups, I think the
answer is yes, since the spin_unlock of desc->lock (release) can
guarantee this though there seems no documentation around
request_irq() to say this.
And I can see at least drivers/video/fbdev/omap2/omapfb/dss/dispc.c is
using smp_wmb() before the request_irq().
And even if write is ordered we still need read to be ordered to be
paired with that.
> if it doesn't it just needs to be fixed, not worked around in
> virtio.
2) virtio drivers might do a lot of setups between request_irq() and
virtio_device_ready():
request_irq()
driver specific setups
virtio_device_ready()
CPU 0 probe) request_irq()
CPU 1 IRQ handler) read the uninitialized variable
CPU 0 probe) driver specific setups
CPU 0 probe) smp_store_release(intr_soft_enabled, true), commit the setups
CPU 1 IRQ handler) read irq_soft_enable as true
CPU 1 IRQ handler) use the uninitialized variable
Thanks
>
>
> > >
> > > > We use smp_store_relase()
> > > > to make sure the driver commits the setup before enabling
the irq. It
> > > > means the read needs to be ordered as well in
vring_interrupt().
> > > >
> > > > >
> > > > > Although I couldn't find anything about this in
memory-barriers.txt
> > > > > which surprises me.
> > > > >
> > > > > CC Paul to help make sure I'm right.
> > > > >
> > > > >
> > > > > >
> > > > > > >
> > > > > > > > To avoid breaking legacy device which
can send IRQ before DRIVER_OK, a
> > > > > > > > module parameter is introduced to enable
the hardening so function
> > > > > > > > hardening is disabled by default.
> > > > > > > Which devices are these? How come they send
an interrupt before there
> > > > > > > are any buffers in any queues?
> > > > > >
> > > > > >
> > > > > > I copied this from the commit log for
22b7050a024d7
> > > > > >
> > > > > > "
> > > > > >
> > > > > > This change will also benefit old hypervisors
(before 2009)
> > > > > > that send interrupts without checking
DRIVER_OK: previously,
> > > > > > the callback could race with driver-specific
initialization.
> > > > > > "
> > > > > >
> > > > > > If this is only for config interrupt, I can remove
the above log.
> > > > >
> > > > >
> > > > > This is only for config interrupt.
> > > >
> > > > Ok.
> > > >
> > > > >
> > > > > >
> > > > > > >
> > > > > > > > Note that the hardening is only done for
vring interrupt since the
> > > > > > > > config interrupt hardening is already
done in commit 22b7050a024d7
> > > > > > > > ("virtio: defer config changed
notifications"). But the method that is
> > > > > > > > used by config interrupt can't be
reused by the vring interrupt
> > > > > > > > handler because it uses spinlock to do
the synchronization which is
> > > > > > > > expensive.
> > > > > > > >
> > > > > > > > Signed-off-by: Jason Wang <jasowang
at redhat.com>
> > > > > > >
> > > > > > > > ---
> > > > > > > > drivers/virtio/virtio.c | 19
+++++++++++++++++++
> > > > > > > > drivers/virtio/virtio_ring.c | 9
++++++++-
> > > > > > > > include/linux/virtio.h | 4
++++
> > > > > > > > include/linux/virtio_config.h | 25
+++++++++++++++++++++++++
> > > > > > > > 4 files changed, 56 insertions(+), 1
deletion(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/virtio/virtio.c
b/drivers/virtio/virtio.c
> > > > > > > > index 8dde44ea044a..85e331efa9cc 100644
> > > > > > > > --- a/drivers/virtio/virtio.c
> > > > > > > > +++ b/drivers/virtio/virtio.c
> > > > > > > > @@ -7,6 +7,12 @@
> > > > > > > > #include <linux/of.h>
> > > > > > > > #include
<uapi/linux/virtio_ids.h>
> > > > > > > > +static bool irq_hardening = false;
> > > > > > > > +
> > > > > > > > +module_param(irq_hardening, bool,
0444);
> > > > > > > > +MODULE_PARM_DESC(irq_hardening,
> > > > > > > > + "Disalbe IRQ software
processing when it is not expected");
> > > > > > > > +
> > > > > > > > /* Unique numbering for virtio
devices. */
> > > > > > > > static DEFINE_IDA(virtio_index_ida);
> > > > > > > > @@ -220,6 +226,15 @@ static int
virtio_features_ok(struct virtio_device *dev)
> > > > > > > > * */
> > > > > > > > void virtio_reset_device(struct
virtio_device *dev)
> > > > > > > > {
> > > > > > > > + /*
> > > > > > > > + * The below synchronize_rcu()
guarantees that any
> > > > > > > > + * interrupt for this line arriving
after
> > > > > > > > + * synchronize_rcu() has completed is
guaranteed to see
> > > > > > > > + * irq_soft_enabled == false.
> > > > > > > News to me I did not know synchronize_rcu has
anything to do
> > > > > > > with interrupts. Did not you intend to use
synchronize_irq?
> > > > > > > I am not even 100% sure synchronize_rcu is by
design a memory barrier
> > > > > > > though it's most likely is ...
> > > > > >
> > > > > >
> > > > > > According to the comment above tree RCU version of
synchronize_rcu():
> > > > > >
> > > > > > """
> > > > > >
> > > > > > * RCU read-side critical sections are delimited
by rcu_read_lock()
> > > > > > * and rcu_read_unlock(), and may be nested. In
addition, but only in
> > > > > > * v5.0 and later, regions of code across which
interrupts, preemption,
> > > > > > * or softirqs have been disabled also serve as
RCU read-side critical
> > > > > > * sections. This includes hardware interrupt
handlers, softirq handlers,
> > > > > > * and NMI handlers.
> > > > > > """
> > > > > >
> > > > > > So interrupt handlers are treated as read-side
critical sections.
> > > > > >
> > > > > > And it has the comment for explain the barrier:
> > > > > >
> > > > > > """
> > > > > >
> > > > > > * Note that this guarantee implies further
memory-ordering guarantees.
> > > > > > * On systems with more than one CPU, when
synchronize_rcu() returns,
> > > > > > * each CPU is guaranteed to have executed a full
memory barrier since
> > > > > > * the end of its last RCU read-side critical
section whose beginning
> > > > > > * preceded the call to synchronize_rcu(). In
addition, each CPU having
> > > > > > """
> > > > > >
> > > > > > So on SMP it provides a full barrier. And for
UP/tiny RCU we don't need the
> > > > > > barrier, if the interrupt come after WRITE_ONCE()
it will see the
> > > > > > irq_soft_enabled as false.
> > > > > >
> > > > >
> > > > > You are right. So then
> > > > > 1. I do not think we need load_acquire - why is it
needed? Just
> > > > > READ_ONCE should do.
> > > >
> > > > See above.
> > > >
> > > > > 2. isn't synchronize_irq also doing the same thing?
> > > >
> > > >
> > > > Yes, but it requires a config ops since the IRQ knowledge is
transport specific.
> > > >
> > > > >
> > > > >
> > > > > > >
> > > > > > > > + */
> > > > > > > > + WRITE_ONCE(dev->irq_soft_enabled,
false);
> > > > > > > > + synchronize_rcu();
> > > > > > > > +
> > > > > > > > dev->config->reset(dev);
> > > > > > > > }
> > > > > > > >
EXPORT_SYMBOL_GPL(virtio_reset_device);
> > > > > > > Please add comment explaining where it will
be enabled.
> > > > > > > Also, we *really* don't need to synch if
it was already disabled,
> > > > > > > let's not add useless overhead to the
boot sequence.
> > > > > >
> > > > > >
> > > > > > Ok.
> > > > > >
> > > > > >
> > > > > > >
> > > > > > >
> > > > > > > > @@ -427,6 +442,10 @@ int
register_virtio_device(struct virtio_device *dev)
> > > > > > > >
spin_lock_init(&dev->config_lock);
> > > > > > > > dev->config_enabled =
false;
> > > > > > > > dev->config_change_pending
= false;
> > > > > > > > + dev->irq_soft_check =
irq_hardening;
> > > > > > > > +
> > > > > > > > + if (dev->irq_soft_check)
> > > > > > > > + dev_info(&dev->dev,
"IRQ hardening is enabled\n");
> > > > > > > > /* We always start by
resetting the device, in case a previous
> > > > > > > > * driver messed it up. This
also tests that code path a little. */
> > > > > > > one of the points of hardening is it's
also helpful for buggy
> > > > > > > devices. this flag defeats the purpose.
> > > > > >
> > > > > >
> > > > > > Do you mean:
> > > > > >
> > > > > > 1) we need something like config_enable? This
seems not easy to be
> > > > > > implemented without obvious overhead, mainly the
synchronize with the
> > > > > > interrupt handlers
> > > > >
> > > > > But synchronize is only on tear-down path. That is not
critical for any
> > > > > users at the moment, even less than probe.
> > > >
> > > > I meant if we have vq->irq_pending, we need to call
vring_interrupt()
> > > > in the virtio_device_ready() and synchronize the IRQ
handlers with
> > > > spinlock or others.
> > > >
> > > > >
> > > > > > 2) enable this by default, so I don't object,
but this may have some risk
> > > > > > for old hypervisors
> > > > >
> > > > >
> > > > > The risk if there's a driver adding buffers without
setting DRIVER_OK.
> > > >
> > > > Probably not, we have devices that accept random inputs from
outside,
> > > > net, console, input etc. I've done a round of audits of
the Qemu
> > > > codes. They look all fine since day0.
> > > >
> > > > > So with this approach, how about we rename the flag
"driver_ok"?
> > > > > And then add_buf can actually test it and BUG_ON if not
there (at least
> > > > > in the debug build).
> > > >
> > > > This looks like a hardening of the driver in the core
instead of the
> > > > device. I think it can be done but in a separate series.
> > > >
> > > > >
> > > > > And going down from there, how about we cache status in
the
> > > > > device? Then we don't need to keep re-reading it
every time,
> > > > > speeding boot up a tiny bit.
> > > >
> > > > I don't fully understand here, actually spec requires
status to be
> > > > read back for validation in many cases.
> > > >
> > > > Thanks
> > > >
> > > > >
> > > > > >
> > > > > > >
> > > > > > > > diff --git
a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > > > > > index 962f1477b1fa..0170f8c784d8 100644
> > > > > > > > --- a/drivers/virtio/virtio_ring.c
> > > > > > > > +++ b/drivers/virtio/virtio_ring.c
> > > > > > > > @@ -2144,10 +2144,17 @@ static inline
bool more_used(const struct vring_virtqueue *vq)
> > > > > > > > return vq->packed_ring ?
more_used_packed(vq) : more_used_split(vq);
> > > > > > > > }
> > > > > > > > -irqreturn_t vring_interrupt(int irq,
void *_vq)
> > > > > > > > +irqreturn_t vring_interrupt(int irq,
void *v)
> > > > > > > > {
> > > > > > > > + struct virtqueue *_vq = v;
> > > > > > > > + struct virtio_device *vdev =
_vq->vdev;
> > > > > > > > struct vring_virtqueue *vq =
to_vvq(_vq);
> > > > > > > > + if (!virtio_irq_soft_enabled(vdev)) {
> > > > > > > > +
dev_warn_once(&vdev->dev, "virtio vring IRQ raised before
DRIVER_OK");
> > > > > > > > + return IRQ_NONE;
> > > > > > > > + }
> > > > > > > > +
> > > > > > > > if (!more_used(vq)) {
> > > > > > > >
pr_debug("virtqueue interrupt with no work for %p\n", vq);
> > > > > > > > return IRQ_NONE;
> > > > > > > > diff --git a/include/linux/virtio.h
b/include/linux/virtio.h
> > > > > > > > index 5464f398912a..957d6ad604ac 100644
> > > > > > > > --- a/include/linux/virtio.h
> > > > > > > > +++ b/include/linux/virtio.h
> > > > > > > > @@ -95,6 +95,8 @@ dma_addr_t
virtqueue_get_used_addr(struct virtqueue *vq);
> > > > > > > > * @failed: saved value for
VIRTIO_CONFIG_S_FAILED bit (for restore)
> > > > > > > > * @config_enabled: configuration
change reporting enabled
> > > > > > > > * @config_change_pending:
configuration change reported while disabled
> > > > > > > > + * @irq_soft_check: whether or not to
check @irq_soft_enabled
> > > > > > > > + * @irq_soft_enabled: callbacks enabled
> > > > > > > > * @config_lock: protects
configuration change reporting
> > > > > > > > * @dev: underlying device.
> > > > > > > > * @id: the device type identification
(used to match it with a driver).
> > > > > > > > @@ -109,6 +111,8 @@ struct virtio_device
{
> > > > > > > > bool failed;
> > > > > > > > bool config_enabled;
> > > > > > > > bool config_change_pending;
> > > > > > > > + bool irq_soft_check;
> > > > > > > > + bool irq_soft_enabled;
> > > > > > > > spinlock_t config_lock;
> > > > > > > > spinlock_t vqs_list_lock; /*
Protects VQs list access */
> > > > > > > > struct device dev;
> > > > > > > > diff --git
a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > > > > > > > index dafdc7f48c01..9c1b61f2e525 100644
> > > > > > > > --- a/include/linux/virtio_config.h
> > > > > > > > +++ b/include/linux/virtio_config.h
> > > > > > > > @@ -174,6 +174,24 @@ static inline bool
virtio_has_feature(const struct virtio_device *vdev,
> > > > > > > > return __virtio_test_bit(vdev,
fbit);
> > > > > > > > }
> > > > > > > > +/*
> > > > > > > > + * virtio_irq_soft_enabled: whether we
can execute callbacks
> > > > > > > > + * @vdev: the device
> > > > > > > > + */
> > > > > > > > +static inline bool
virtio_irq_soft_enabled(const struct virtio_device *vdev)
> > > > > > > > +{
> > > > > > > > + if (!vdev->irq_soft_check)
> > > > > > > > + return true;
> > > > > > > > +
> > > > > > > > + /*
> > > > > > > > + * Read irq_soft_enabled before
reading other device specific
> > > > > > > > + * data. Paried with
smp_store_relase() in
> > > > > > > paired
> > > > > >
> > > > > >
> > > > > > Will fix.
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > > + * virtio_device_ready() and
WRITE_ONCE()/synchronize_rcu() in
> > > > > > > > + * virtio_reset_device().
> > > > > > > > + */
> > > > > > > > + return
smp_load_acquire(&vdev->irq_soft_enabled);
> > > > > > > > +}
> > > > > > > > +
> > > > > > > > /**
> > > > > > > > * virtio_has_dma_quirk - determine
whether this device has the DMA quirk
> > > > > > > > * @vdev: the device
> > > > > > > > @@ -236,6 +254,13 @@ void
virtio_device_ready(struct virtio_device *dev)
> > > > > > > > if
(dev->config->enable_cbs)
> > > > > > > >
dev->config->enable_cbs(dev);
> > > > > > > > + /*
> > > > > > > > + * Commit the driver setup before
enabling the virtqueue
> > > > > > > > + * callbacks. Paried with
smp_load_acuqire() in
> > > > > > > > + * virtio_irq_soft_enabled()
> > > > > > > > + */
> > > > > > > > +
smp_store_release(&dev->irq_soft_enabled, true);
> > > > > > > > +
> > > > > > > > BUG_ON(status &
VIRTIO_CONFIG_S_DRIVER_OK);
> > > > > > > >
dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
> > > > > > > > }
> > > > > > > > --
> > > > > > > > 2.25.1
> > > > >
> > >
>