Hi,
AlexHully wrote:
Could userspace still being considered userspace if it doesn't mess with the kernel virtual space but use DPL 0 permission (it can alter interrupt states and so on)?
Yes; it could still be considered user space (but couldn't be considered secure, unless the OS is doing something else to ensure isolation - e.g. managed code).
Don't forget that you could set IOPL=3 to allow CPL=3 tasks to use some things (HLT, CLI/STI, IO ports) without given them full access to things like CR0, CR3, MSRs, etc.
Cheers,
Brendan