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Subjectxen: Fix possible page fault in fifo events
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Date
sync_test_bit function require a long* read access to pointer.
This is a problem if the you are using last entry in the page causing
an access to next page. If this page is not readable you get a memory
access failure (page fault).
All other x64 bit functions access memory using 32 bit operations.
For processors different than x64 long aligned operations are used.

Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
---
drivers/xen/events/events_fifo.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index d302639..af4672d 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -168,6 +168,11 @@ static int evtchn_fifo_setup(struct irq_info *info)
return ret;
}

+static __always_inline int test_fifo_bit(int nr, event_word_t *word)
+{
+ return (ACCESS_ONCE(*word) & (((event_word_t) 1) << nr)) != 0;
+}
+
static void evtchn_fifo_bind_to_cpu(struct irq_info *info, unsigned cpu)
{
/* no-op */
@@ -188,7 +193,7 @@ static void evtchn_fifo_set_pending(unsigned port)
static bool evtchn_fifo_is_pending(unsigned port)
{
event_word_t *word = event_word_from_port(port);
- return sync_test_bit(EVTCHN_FIFO_BIT(PENDING, word), BM(word));
+ return test_fifo_bit(EVTCHN_FIFO_PENDING, word);
}

static bool evtchn_fifo_test_and_set_mask(unsigned port)
@@ -206,7 +211,7 @@ static void evtchn_fifo_mask(unsigned port)
static bool evtchn_fifo_is_masked(unsigned port)
{
event_word_t *word = event_word_from_port(port);
- return sync_test_bit(EVTCHN_FIFO_BIT(MASKED, word), BM(word));
+ return test_fifo_bit(EVTCHN_FIFO_MASKED, word);
}
/*
* Clear MASKED, spinning if BUSY is set.
--
1.9.1



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