SEBI has introduced ASM to basically control volatility, while GSM is used to safeguard investors against stocks which may be moving out of line with fundamentals.
In order to enhance market integrity and safeguard the interest of investors, Securities and Exchange Board of India (SEBI) and Exchanges, have been introducing various enhanced surveillance measures such as reduction in price band, periodic call auction and transfer of securities into Trade to Trade segment from time to time.
While placing an order for security under GSM list, user shall need to provide consent for placing the order.
To know the stocks which are currently under GSM, check out below page on the NSE website https://www.nseindia.com/reports/gsm
To know the criteria for the inclusion of securities under the GSM framework, refer to this FAQ.