From the Apple Support Page:
This update resolves an issue where a MacBook Pro being used with a power adapter may unexpectedly shut down under heavy workload if the battery charge level is near empty.
Your computer’s power cord must be connected and plugged into a working power source, or your battery must be at least 25% charged.
When your computer restarts a gray screen will appear with a status bar to indicate the progress of the update.
Your computer’s fans will run at full speed during the update but will return to normal speed once the update completes.
Do not disturb or shut off the power on your computer during this update.
The firmware update can be downloaded from the Apple Support Website.
More information about the update can also be viewed on the Apple Support Website “About the SMC Firmware Update” page.
The update applies to MacBook Pro models 8,1, 8,2, and 8,3. These include both MacBook Pro (Early 2011) and MacBook Pro (Late 2011).