Re: Accelerating user mode linux

[Alan Cox]

> can't be an interrupt in the middle of that sequence.  So, sys_switchmm
> would also have to restore the old signal mask, which you'd have to pass
> in unless you're going to read it off the signal frame.  Also, it would
> have to be open coded because you've already restored the stack pointer.

Uggh.. you are right. You end up needing sigreturn handling

> Your objection to returning through sigreturn was performance.  Is performance
> a veto of adding an mm switch to sigreturn, or it is possible to make it
> acceptible?

Its not a veto. I was trying to avoid having to add any more branches to
the fast paths in the kernel.  The remaining sigreturn question is 
"how do you get into 'user' mode the first time"