From fed1755b118147721f2c87b37b9d66e62c39b668 Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Mon, 14 Dec 2020 10:02:45 +0100 Subject: xen/xenbus: Allow watches discard events before queueing If handling logics of watch events are slower than the events enqueue logic and the events can be created from the guests, the guests could trigger memory pressure by intensively inducing the events, because it will create a huge number of pending events that exhausting the memory. Fortunately, some watch events could be ignored, depending on its handler callback. For example, if the callback has interest in only one single path, the watch wouldn't want multiple pending events. Or, some watches could ignore events to same path. To let such watches to volutarily help avoiding the memory pressure situation, this commit introduces new watch callback, 'will_handle'. If it is not NULL, it will be called for each new event just before enqueuing it. Then, if the callback returns false, the event will be discarded. No watch is using the callback for now, though. This is part of XSA-349 Cc: stable@vger.kernel.org Signed-off-by: SeongJae Park Reported-by: Michael Kurth Reported-by: Pawel Wieczorkiewicz Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross --- include/xen/xenbus.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'include') diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h index 5a8315e6d8a6..baa88bf0b9bc 100644 --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -61,6 +61,13 @@ struct xenbus_watch /* Path being watched. */ const char *node; + /* + * Called just before enqueing new event while a spinlock is held. + * The event will be discarded if this callback returns false. + */ + bool (*will_handle)(struct xenbus_watch *, + const char *path, const char *token); + /* Callback (executed in a process context with no locks held). */ void (*callback)(struct xenbus_watch *, const char *path, const char *token); -- cgit v1.2.3 From 2e85d32b1c865bec703ce0c962221a5e955c52c2 Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Mon, 14 Dec 2020 10:04:18 +0100 Subject: xen/xenbus: Add 'will_handle' callback support in xenbus_watch_path() Some code does not directly make 'xenbus_watch' object and call 'register_xenbus_watch()' but use 'xenbus_watch_path()' instead. This commit adds support of 'will_handle' callback in the 'xenbus_watch_path()' and it's wrapper, 'xenbus_watch_pathfmt()'. This is part of XSA-349 Cc: stable@vger.kernel.org Signed-off-by: SeongJae Park Reported-by: Michael Kurth Reported-by: Pawel Wieczorkiewicz Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross --- include/xen/xenbus.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h index baa88bf0b9bc..c8574d1b814c 100644 --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -204,10 +204,14 @@ void xenbus_probe(struct work_struct *); int xenbus_watch_path(struct xenbus_device *dev, const char *path, struct xenbus_watch *watch, + bool (*will_handle)(struct xenbus_watch *, + const char *, const char *), void (*callback)(struct xenbus_watch *, const char *, const char *)); -__printf(4, 5) +__printf(5, 6) int xenbus_watch_pathfmt(struct xenbus_device *dev, struct xenbus_watch *watch, + bool (*will_handle)(struct xenbus_watch *, + const char *, const char *), void (*callback)(struct xenbus_watch *, const char *, const char *), const char *pathfmt, ...); -- cgit v1.2.3 From 3dc86ca6b4c8cfcba9da7996189d1b5a358a94fc Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Mon, 14 Dec 2020 10:07:13 +0100 Subject: xen/xenbus: Count pending messages for each watch This commit adds a counter of pending messages for each watch in the struct. It is used to skip unnecessary pending messages lookup in 'unregister_xenbus_watch()'. It could also be used in 'will_handle' callback. This is part of XSA-349 Cc: stable@vger.kernel.org Signed-off-by: SeongJae Park Reported-by: Michael Kurth Reported-by: Pawel Wieczorkiewicz Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross --- include/xen/xenbus.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h index c8574d1b814c..00c7235ae93e 100644 --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -61,6 +61,8 @@ struct xenbus_watch /* Path being watched. */ const char *node; + unsigned int nr_pending; + /* * Called just before enqueing new event while a spinlock is held. * The event will be discarded if this callback returns false. -- cgit v1.2.3