How to communicate between rings?

[bingmatv]

User-space programs should run in CPU ring3, but kernel runs in ring0, how to communicate between rings?

[bjorn3]

The kernel can go to userspace using iret/sysret and userspace can call into the kernel using the syscall instruction or by causing an exception.

[ViktorPopp]

The kernel can go to userspace using iret/sysret and userspace can call into the kernel using the syscall instruction or by causing an exception.

What is needed to do before userspace and what are the best resources @bjorn3 ?

[bjorn3]

Maybe https://wiki.osdev.org/Getting_to_Ring_3 would help you?

[ChocolateLoverRaj]

• https://nfil.dev/kernel/rust/coding/rust-kernel-to-userspace-and-back/
• https://github.com/nikofil/rust-os

My OS: https://github.com/ChocolateLoverRaj/code-runner/tree/edition-3. Note that I am still working on the ELF stuff.

[bingmatv]

Does userspace run slower than or as fast as kernelspace? Since userspace has less privilege, the hardware or kernel needs to check the privilege.

[bjorn3]

Same speed. Only transitions between rings are relatively slow (couple hundred cycles if you optimize our kernel a bit).