> Many hardware platforms that have TPM, have it connected via a low-bandwidth LPC bus which would have nowhere near enough bandwidth for demand decryption/encryption of memory pages.
Ah, of course. I was more thinking along the lines of "CPU loads the key for decrypting RAM directly from the TMP into registers, and reloads it from there after waking from suspend or after a task switch has refilled those registers".
I don't know exactly how long loading value from a TPM takes, but my gut says it would be much too long to do it on task switch. Almost certainly fine for waking up from suspend though. Also the problem that physical TPMs communicate with the CPU over plaintext and TPMs in general, including fTPMs, have had notable vulnerabilities.