Intel's Dynamic PAMT Appears Ready For Linux 7.4 To Help With TDX Memory Overhead

Intel's Dynamic PAMT feature looks like it's finally going to be ready for mainline with Linux 7.4. The Intel Dynamic PAMT is used for helping to reduce memory overhead when making use of Trusted Domain Extensions (TDX) for confidential VMs. Being worked on for the Linux kernel over the past year is Dynamic PAMT for lowering the memory overhead of TDX. TDX needs to keep data on each physical page it uses and amounts to around 0.4% of the system memory. Dynamic PAMT frees up some of that memory overhead, which can be significant with modern high-end servers into terabytes of memory. And memory prices being what they are today, who wants to waste any amount of RAM if it can be avoided. Now queued into tip/tip.git's x86/tdx Git branch are the Dynamic PAMT enablement patches. With the patches now in a TIP branch, they should be merged for the next merge window: Linux 7.4. With these to-be-merged patches, Dynamic PAMT will be enabled by default where supported on Intel TDX servers. The enabling commit explains: "The Physical Address Metadata Table (PAMT) holds TDX metadata for physical memory and must be allocated by the kernel during TDX module initialization. Dynamic PAMT (DPAMT) is a TDX module feature that can reduce this memory use by allocating part of the PAMT dynamically. DPAMT's memory savings are significant enough to make it a good default configuration. So turn it on whenever the TDX module reports support. ... The feature increases the kernel size by 2KB (when TDX is configured in the build)." Good to see Dynamic PAMT finally on its way to being used -- and by default -- with Linux.