[PATCH AUTOSEL 5.10 24/45] xen: Fix event channel callback via INTX/GSI

Sasha Levin
2021-01-20T02:36:21Z

From: David Woodhouse <dwmw@amazon.co.uk>

[ Upstream commit 3499ba8198cad47b731792e5e56b9ec2a78a83a2 ]

For a while, event channel notification via the PCI platform device
has been broken, because we attempt to communicate with xenstore before
we even have notifications working, with the xs_reset_watches() call
in xs_init().

We tend to get away with this on Xen versions below 4.0 because we avoid
calling xs_reset_watches() anyway, because xenstore might not cope with
reading a non-existent key. And newer Xen *does* have the vector
callback support, so we rarely fall back to INTX/GSI delivery.

To fix it, clean up a bit of the mess of xs_init() and xenbus_probe()
startup. Call xs_init() directly from xenbus_init() only in the !XS_HVM
case, deferring it to be called from xenbus_probe() in the XS_HVM case
instead.

Then fix up the invocation of xenbus_probe() to happen either from its
device_initcall if the callback is available early enough, or when the
callback is finally set up. This means that the hack of calling
xenbus_probe() from a workqueue after the first interrupt, or directly
from the PCI platform device setup, is no longer needed.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20210113132606.422794-2-dwmw2@infradead.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm/xen/enlighten.c | 2 +-
drivers/xen/events/events_base.c | 10 ----
drivers/xen/platform-pci.c | 1 -
drivers/xen/xenbus/xenbus.h | 1 +
drivers/xen/xenbus/xenbus_comms.c | 8 ---
drivers/xen/xenbus/xenbus_probe.c | 81 +++++++++++++++++++++++++------
include/xen/xenbus.h | 2 +-
7 files changed, 70 insertions(+), 35 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 60e901cd0de6a..5a957a9a09843 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -371,7 +371,7 @@ static int __init xen_guest_init(void)
}
gnttab_init();
if (!xen_initial_domain())
- xenbus_probe(NULL);
+ xenbus_probe();

/*
* Making sure board specific code will not set up ops for
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 6038c4c35db5a..bbebe248b7264 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -2010,16 +2010,6 @@ static struct irq_chip xen_percpu_chip __read_mostly = {
.irq_ack = ack_dynirq,
};

-int xen_set_callback_via(uint64_t via)
-{
- struct xen_hvm_param a;
- a.domid = DOMID_SELF;
- a.index = HVM_PARAM_CALLBACK_IRQ;
- a.value = via;
- return HYPERVISOR_hvm_op(HVMOP_set_param, &a);
-}
-EXPORT_SYMBOL_GPL(xen_set_callback_via);
-
#ifdef CONFIG_XEN_PVHVM
/* Vector callbacks are better than PCI interrupts to receive event
* channel notifications because we can receive vector callbacks on any
diff --git a/drivers/xen/platform-pci.c b/drivers/xen/platform-pci.c
index dd911e1ff782c..9db557b76511b 100644
--- a/drivers/xen/platform-pci.c
+++ b/drivers/xen/platform-pci.c
@@ -149,7 +149,6 @@ static int platform_pci_probe(struct pci_dev *pdev,
ret = gnttab_init();
if (ret)
goto grant_out;
- xenbus_probe(NULL);
return 0;
grant_out:
gnttab_free_auto_xlat_frames();
diff --git a/drivers/xen/xenbus/xenbus.h b/drivers/xen/xenbus/xenbus.h
index 2a93b7c9c1599..dc15373354144 100644
--- a/drivers/xen/xenbus/xenbus.h
+++ b/drivers/xen/xenbus/xenbus.h
@@ -115,6 +115,7 @@ int xenbus_probe_node(struct xen_bus_type *bus,
const char *type,
const char *nodename);
int xenbus_probe_devices(struct xen_bus_type *bus);
+void xenbus_probe(void);

void xenbus_dev_changed(const char *node, struct xen_bus_type *bus);

diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index eb5151fc8efab..e5fda0256feb3 100644
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -57,16 +57,8 @@ DEFINE_MUTEX(xs_response_mutex);
static int xenbus_irq;
static struct task_struct *xenbus_task;

-static DECLARE_WORK(probe_work, xenbus_probe);
-
-
static irqreturn_t wake_waiting(int irq, void *unused)
{
- if (unlikely(xenstored_ready == 0)) {
- xenstored_ready = 1;
- schedule_work(&probe_work);
- }
-
wake_up(&xb_waitq);
return IRQ_HANDLED;
}
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 44634d970a5ca..c8f0282bb6497 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -683,29 +683,76 @@ void unregister_xenstore_notifier(struct notifier_block *nb)
}
EXPORT_SYMBOL_GPL(unregister_xenstore_notifier);

-void xenbus_probe(struct work_struct *unused)
+void xenbus_probe(void)
{
xenstored_ready = 1;

+ /*
+ * In the HVM case, xenbus_init() deferred its call to
+ * xs_init() in case callbacks were not operational yet.
+ * So do it now.
+ */
+ if (xen_store_domain_type == XS_HVM)
+ xs_init();
+
/* Notify others that xenstore is up */
blocking_notifier_call_chain(&xenstore_chain, 0, NULL);
}
-EXPORT_SYMBOL_GPL(xenbus_probe);

-static int __init xenbus_probe_initcall(void)
+/*
+ * Returns true when XenStore init must be deferred in order to
+ * allow the PCI platform device to be initialised, before we
+ * can actually have event channel interrupts working.
+ */
+static bool xs_hvm_defer_init_for_callback(void)
{
- if (!xen_domain())
- return -ENODEV;
+#ifdef CONFIG_XEN_PVHVM
+ return xen_store_domain_type == XS_HVM &&
+ !xen_have_vector_callback;
+#else
+ return false;
+#endif
+}

- if (xen_initial_domain() || xen_hvm_domain())
- return 0;
+static int __init xenbus_probe_initcall(void)
+{
+ /*
+ * Probe XenBus here in the XS_PV case, and also XS_HVM unless we
+ * need to wait for the platform PCI device to come up.
+ */
+ if (xen_store_domain_type == XS_PV ||
+ (xen_store_domain_type == XS_HVM &&
+ !xs_hvm_defer_init_for_callback()))
+ xenbus_probe();

- xenbus_probe(NULL);
return 0;
}
-
device_initcall(xenbus_probe_initcall);

+int xen_set_callback_via(uint64_t via)
+{
+ struct xen_hvm_param a;
+ int ret;
+
+ a.domid = DOMID_SELF;
+ a.index = HVM_PARAM_CALLBACK_IRQ;
+ a.value = via;
+
+ ret = HYPERVISOR_hvm_op(HVMOP_set_param, &a);
+ if (ret)
+ return ret;
+
+ /*
+ * If xenbus_probe_initcall() deferred the xenbus_probe()
+ * due to the callback not functioning yet, we can do it now.
+ */
+ if (!xenstored_ready && xs_hvm_defer_init_for_callback())
+ xenbus_probe();
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(xen_set_callback_via);
+
/* Set up event channel for xenstored which is run as a local process
* (this is normally used only in dom0)
*/
@@ -818,11 +865,17 @@ static int __init xenbus_init(void)
break;
}

- /* Initialize the interface to xenstore. */
- err = xs_init();
- if (err) {
- pr_warn("Error initializing xenstore comms: %i\n", err);
- goto out_error;
+ /*
+ * HVM domains may not have a functional callback yet. In that
+ * case let xs_init() be called from xenbus_probe(), which will
+ * get invoked at an appropriate time.
+ */
+ if (xen_store_domain_type != XS_HVM) {
+ err = xs_init();
+ if (err) {
+ pr_warn("Error initializing xenstore comms: %i\n", err);
+ goto out_error;
+ }
}

if ((xen_store_domain_type != XS_LOCAL) &&
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 00c7235ae93e7..2c43b0ef1e4d5 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -192,7 +192,7 @@ void xs_suspend_cancel(void);

struct work_struct;

-void xenbus_probe(struct work_struct *);
+void xenbus_probe(void);

#define XENBUS_IS_ERR_READ(str) ({ \
if (!IS_ERR(str) && strlen(str) == 0) { \
--
2.27.0