Memory device security and row hammer mitigation

1. A method, comprising:

receiving a row activation command having a row address at control circuitry of a memory sub-system;

incrementing a first count of a row counter corresponding to the row address stored in a content addressable memory (CAM) of the memory sub-system;

determining, at the control circuitry, whether the first count is greater than a row hammer threshold (RHT) minus a second count of a CAM decrease counter (CDC), wherein the second count is incremented each time the CAM is full; and

responsive to determining that the first count is greater than the RHT minus the second count, issuing a refresh command to the row address.

2. The method of claim 1 , further comprising, responsive to determining that the first count is greater than the RHT minus the second count, deleting the row counter corresponding to the row address from the CAM.

3. The method of claim 1 , further comprising initializing a plurality of CDCs including the CDC to 0 prior to receipt of the row activation command.

4. The method of claim 1 , wherein incrementing the first count of the row counter includes incrementing the first count of the row counter responsive to determining that the row counter is stored in the CAM.

5. The method of claim 1 , further comprising setting a size of the CAM based on a frequency target for row activation commands.

6. The method of claim 1 , further comprising setting a size of the CAM based on a frequency target for row activation commands that is less than the RHT.

7. The method of claim 1 , further comprising setting a size of the CAM based on a maximum quantity of row activations for a particular period.

8. An apparatus, comprising:

a content addressable memory (CAM);

a memory device; and

control circuitry coupled to the memory device and configured to:

receive a row activation command having a row address of the memory device;

responsive to determining that a row counter corresponding to the row address is stored in the CAM, increment a first count of the row counter;

determine whether the first count is greater than a row hammer threshold (RHT) minus a second count of a CAM decrease counter (CDC), wherein the CDC stores a quantity of times different row addresses have been unassociated with the CAM once the CAM is full; and

responsive to determining that the first count is greater than the RHT minus the second count, issue a refresh command to the row address.

9. The apparatus of claim 8 , wherein the control circuitry is further configured to determine whether the CAM has space to store the row counter responsive to determining that the row counter is not stored in the CAM.

10. The apparatus of claim 9 , wherein the control circuitry is further configured to, responsive to determining that the CAM has space to store the row counter, store the row counter in the CAM.

11. The apparatus of claim 9 , wherein the control circuitry is further configured to, responsive to determining that the CAM does not have space to store the row counter, decrement a plurality of counts of the CAM including the first count.

12. The apparatus of claim 11 , wherein the control circuitry is further configured to, responsive to determining that the CAM does not have space to store the row counter, delete any of the plurality of counts that have a zero value to unassociated a particular row corresponding to a deleted count with the CAM.

13. The apparatus of claim 11 , wherein the control circuitry is further configured to, responsive to determining that the CAM does not have space to store the counter, increment the second count of the CDC.

14. An apparatus, comprising:

a content addressable memory (CAM);

a memory device;

control circuitry coupled to the memory device and configured to:

receive a row activation command directed to a row address of the memory device;

determine whether a row counter corresponding to the row address is stored in the CAM;

responsive to determining that the row counter corresponding to the row address is stored in the CAM, determine whether a first count of the row counter is greater than a difference between a row hammer threshold (RHT) and a second count of a CAM decrease counter (CDC), wherein the CDC stores a quantity of times different row addresses have been unassociated with the CAM once the CAM is full; and

responsive to determining that the first count is greater than the difference between the RHT and the second count, issue a refresh command to the row address.

15. The apparatus of claim 14 , wherein the control circuitry is further configured to delete the row counter corresponding to the row address from the CAM responsive to determining that the first count is greater than the difference between the RHT and the second count.

16. The apparatus of claim 14 , wherein the control circuitry is further configured to, subsequent to determining that the row counter corresponding to the row address is not stored in the CAM, determine whether the CAM has space to store the row counter.

17. The apparatus of claim 16 , wherein the control circuitry is further configured to, responsive to determining that the CAM does not have space to store the row counter, decrement a plurality of counts of a plurality of row counters stored in the CAM.

18. The apparatus of claim 17 , wherein the control circuitry is further configured to, responsive to decrementing the plurality of counts, determine whether any of the plurality of counts is equal to 0.

19. The apparatus of claim 18 , wherein the control circuitry is further configured to, responsive to determining that at least one count of the plurality of counts is equal to 0, delete a corresponding row counter from the CAM.

20. The apparatus of claim 19 , wherein the control circuitry is further configured to, responsive to deleting the corresponding row counter from the CAM, increment the second count of the CDC.