Kernel: RDNA, Graphics, Bootlin's Work, and LWN

posted by Roy Schestowitz on Jul 18, 2024

• AMD Pushes Out Last Bits of RDNA 4 GPU Enablement Patches At Linux, On-Launch Support Becomes Imminent Now

  Well, Team Red's consistency with RDNA 4 GPUs at Linux was indeed something to appreciate, considering that AMD did get on early with ensuring that the next-gen "RX 8000" series GPUs are fully compatible with Linux out of the box, and it looks like the firm has been able to achieve this.

• Simon Ser: Status update, July 2024

  Hi!

  This month wlroots 0.18.0 has been released! This new version includes a fair share of niceties: ICC profiles, GPU reset recovery, less black screens when plugging in a monitor on Intel, a whole bunch of new protocol implementations, and much more. Thanks a lot to all contributors! Two recent merge requests made it in the release: Kenny’s Vulkan renderer optimizations, and support for the SIZE_HINTS KMS property to use a smaller cursor plane on defective chip maker Intel to save power.

• Linux 6.10 released, Bootlin contributions inside

  Linux 6.10 was released last Sunday, following its now well-known release cadence. As usual, head over to LWN.net to have some good summary of the important features merged in this kernel release: part 1 and part 2.

• Another try for getrandom() in the vDSO

  Random numbers, it seems, can never be random enough, and they cannot be generated quickly enough. The kernel's getrandom() system call might, after years of discussion, be seen as sufficiently secure by most users, but it is still a system call. Linux system calls are relatively fast, but they are necessarily slower than calling a function directly. In an attempt to speed the provision of secure random data to user space, Jason Donenfeld has put together an implementation of getrandom() that lives in the virtual dynamic shared object (vDSO) area.

  Random data is used in no end of applications, including modeling of natural phenomena, generation of identifiers like UUIDs, and game play; it's how NetHack somehow summons those three balrogs all in one corner of a dark room. Security-related operations, such as the generation of nonces and keys, also make heavy use of random data — and depend heavily on that data actually being random. Some applications need so much random data that they spend a significant amount of time in the getrandom() system call.

  One possible solution to this problem is to generate random numbers in user space, perhaps seeded by random data from the kernel; many developers have taken that route over the years. But, as Donenfeld explains in the cover letter to his patch series, that approach is not ideal. The kernel has the best view of the amount of entropy in the system and what is needed to generate truly random data. It is also aware of events, such as virtual-machine forks, that can compromise a random-number generator and make a reseeding necessary

• Offload-friendly network encryption in the kernel

  The PSP security protocol (PSP) is a way to transparently encrypt packets by efficiently offloading encryption and decryption to the network interface cards (NICs) that Google uses for connections inside its data centers. The protocol is similar to IPsec, in that it allows for wrapping arbitrary traffic in a layer of encryption. The difference is that PSP is encapsulated in UDP, and designed from the beginning to reduce the amount of state that NICs have to track in order to send and receive encrypted traffic, allowing for more simultaneous connections. Jakub Kicinski wants to add support for the protocol to the Linux kernel.

• A new API for tree-in-dcache filesystems

  There are a number of kernel filesystems that store their directory entries directly in the directory-entry cache (dcache) without having any permanent storage for those objects. It started out as a "neat hack" for ramfs, Al Viro said, at the start of his filesystem-track session at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit. Unfortunately, as the use of this technique has grown into other filesystems, there has been a lot of scope creep that has gotten out of control. He wanted to discuss some new infrastructure that he is working on to try to clean some of that up.

• Improving pseudo filesystems

  The eventfs filesystem provides an interface to the tracepoints that are available to be used by various Linux tracing tools (e.g. ftrace, perf, uprobes, etc.); it is meant to be a version of the tracefs filesystem that dynamically allocates its entries as needed. The goal is to reduce the memory required for multiple instances of tracefs, as Steven Rostedt described in a session at the 2022 Linux Storage, Filesystem, Memory Management, and BPF Summit. He returned to the 2024 edition of the summit to talk further about how to make pseudo (or virtual) filesystems, such as tracefs/eventfs, more like regular Linux filesystems, where the directory entries (dentries) and inodes are only created (and cached) as needed.

• Giving bootloaders the boot with nmbl

  At DevConf.cz 2024, Marta Lewandowska gave a talk to discuss a new approach for booting Linux systems, "No more boot loader: Please use the kernel instead". The talk, available on YouTube, introduced a new project called nmbl (for "no more bootloader", pronounced "nimble"). The idea is to get rid of bootloaders (e.g., GNU GRUB) with a Unified Kernel Image (UKI) that removes the need for a separate bootloader altogether. It is early days for nmbl, currently the project is only being tested for use with virtual machines, but the idea is compelling. If successful, nmbl could offer security, performance, and maintenance benefits compared to GRUB and other separate bootloaders.