drm/i915: prevent division by zero when asking for chipset power

This prevents an in-kernel division by zero which happens when we are
asking for i915_chipset_val too quickly, or within a race condition
between the power monitoring thread and userspace accesses via debugfs.

The issue can be reproduced easily via the following command:
while ``; do cat /sys/kernel/debug/dri/0/i915_emon_status; done

This is particularly dangerous because it can be triggered by
a non-privileged user by just reading the debugfs entry.

This issue was also found independently by Konstantin Belousov
<[email protected]>, who proposed a similar patch.

Reported-by: Konstantin Belousov <[email protected]>
Acked-by: Jesse Barnes <[email protected]>
Acked-by: Keith Packard <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Cc: <[email protected]>
Signed-off-by: Eugeni Dodonov <[email protected]>
Signed-off-by: Keith Packard <[email protected]>

0 files changed, 0 insertions, 0 deletions