If I understand the description correction this is a little like the
virtual DSO (VDSO) in reverse.
The VDSO method is to provide a virtual library ... a kernel page containing
some userspace code ... which is mapped into the address space of every
process. These process can than access certain system functions (via SYSENTER on x86 processors that support it) without making system calls (via int 0x80H on x86). (On other x86 CPUs the virtual library page can be be implemented as old int 0x80H calls if necessary).
This patch allows a userspace process to register a pointer into its memory ... later allowing the kernel to peek into that memory region to find any futexes that are locked. So you suffer on system call and then the rest of the operations are memory accesses (and the kernel knows when to look in process space for them, and where to look).
Is that the gist of it?
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