A Qualified Mortgage Loan is designed to offer a safer financial product (think back to 2008). The QM Loan was born from that financial crisis in order to prevent history from repeating itself. It requires lenders to verify a borrower's ability to repay and prohibits any loan features that increase the risk of default (i.e. interest-only payments, negative amortization, or balloon payments).  

Before the 2008 financial crisis, there was no 'Qualified Mortgage' rule. A Qualified Mortgage simply means that your mortgage meets the specific federal requirements established by the Consumer Financial Protection Bureau as defined here: https://www.consumerfinance.gov/ask-cfpb/what-is-a-qualified-mortgage-en-1789/

One is able to confirm for themselves if their mortgage is indeed qualified (most are). The Closing Disclosure signed at the time of your loan's closing may be reviewed. If your loan is a 30-year mortgage (loans exceeding this amount i.e. a 40 year+ mortgage are automatically disqualified from being a standard QM) and features no balloon payments, interest-only periods, or negative amortization (https://www.consumerfinance.gov/ask-cfpb/what-is-negative-amortization-en-103/), it is most likely a QM. 

If your loan is an FHA, VA, or USDA loan, it is considered a QM by definition. If a loan is sold to Fannie Mae or Freddie Mac, it is required to meet QM standards to be eligible for purchase by them. 

One may always contact their mortgage servicer and ask for a copy of your Loan Origination file. You can ask: "Was this loan originated as a Qualified Mortgage?" 

Keep in mind that the Qualified Mortgage rule was established also to protect LENDERS from lawsuits regarding the Ability-to-Repay rule (https://www.consumerfinance.gov/ask-cfpb/what-is-the-ability-to-repay-rule-en-1787/). This is incentive for lenders to ensure their loans meet these criteria. 

Non-Qualified Mortgages (Non-QM) include loan types such as bank statement loans, debt service coverage ratio loans (DSCR), interest-only mortgages, asset-depletion loans (https://themortgagereports.com/68921/asset-depletion-mortgage-how-it-works), and jumbo loans that exceed the federal limits or have features such as balloon payments, negative amortization, or terms exceeding 30 years.