[$] Peer-to-peer DMA

In a plenary session on the first day of the 2023 Linux Storage, Filesystem,Memory-Management and BPF Summit, Stephen Bates led a discussion about peer-to-peer DMA (P2PDMA). The idea is toremove the host system's participation in a transfer of data from onePCIe-connected device to another. The feature was originally aimed at NVMeSSDs so that data could simply be copied directly to and from the storagedevice without needing to move it to system memory and then fromthere to somewhere else.