Re: [PATCH v2] x86: Return to kernel without IRET

[Linus Torvalds]

On Fri, May 2, 2014 at 4:53 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On my box, this saves about 100ns on each interrupt and trap that
> happens while running in kernel space.  This speeds up my kernel_pf
> microbenchmark by about 17%.

Btw, would you mind _trying_ to do a similar trick for the "return to
user space" case?

At least as a proof-of-concept, having a code sequence in user mode
trampoline that does

   popq %rsi
   popq %r11
   retq $128

and building up a stack in user space at '%rsp-128' that has the
values or rsi/r11/rip should allow us to use 'sysret'. Hmm?

            Linus
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