Support for Syscall User Dispatch appears to need to be built into the Linux 5.11 kernel. This feature is important for modern Windows games running Linux under Wine / Proton.
Syscall User Dispatch has been in the works for some time as a kernel level enhancement to handle Windows games / applications that use system call instructions, bypassing the Windows API. Games avoiding the Windows API and making system calls directly are increasingly common in modern Windows games, seemingly in the name of digital rights management schemes and similar protected modes. This was, however, an issue for Wine (and Steam Play’s Proton) when bypassing conventional Windows APIs.
Syscall User Dispatch can efficiently redirect system calls and only do it for part of the binary. System calls can be redirected to user space so that they can be handled by Wine. Activation of Syscall User Dispatch is done through a PRCTL interface with per-threaded controls for the behavior of attempted system calls – allowing toggling between running a Windows binary or returning to Wine. More details on the implementation can be found via the Documentation.
Looks like “SUD” was ready for the mainline and now this morning the patches have been inserted into the kernel / entry of tip.git code following all appropriate patch approvals.
So, barring any last minute issues, this month when the Linux 5.11 merge window opens, it should be moved to the mainline for this next cycle. Linux 5.11 stable is expected to be released in February with this feature and more.