Kernel stacks that re freed, can be placed on an SLIST for quick reuse. The old code was using a member of the PFN of the last stack page as the SLIST_ENTRY. This relies on the following (non-portable) assumptions:
- A stack always has a PTE associated with it.
- This PTE has a PFN associated with it.
- The PFN has an empty field that can be re-used as an SLIST_ENTRY.
- The PFN has another field that points back to the PTE, which then can be used to get the stack base.
Specifically: On x64 the PFN field is not 16 bytes aligned, so it cannot be used as an SLIST_ENTRY. (In a "usermode kernel" the other assumptions are also invalid).
The new code does what Windows does (and which seems absolutely obvious to do): Place the SLIST_ENTRY directly on the stack.
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