RE: [PATCH v7 23/33] x86/fred: let ret_from_fork() jmp to fred_exit_user when FRED is enabled

Li, Xin3
2023-04-10T18:31:47Z

> On 4/4/23 03:27, Xin Li wrote:
> > --- a/arch/x86/entry/entry_64.S
> > +++ b/arch/x86/entry/entry_64.S
> > @@ -299,7 +299,12 @@ SYM_CODE_START_NOALIGN(ret_from_fork)
> > UNWIND_HINT_REGS
> > movq %rsp, %rdi
> > call syscall_exit_to_user_mode /* returns with IRQs disabled */
> > +#ifdef CONFIG_X86_FRED
> > + ALTERNATIVE "jmp swapgs_restore_regs_and_return_to_usermode", \
> > + "jmp fred_exit_user", X86_FEATURE_FRED #else
> > jmp swapgs_restore_regs_and_return_to_usermode
> > +#endif
>
> Does the #ifdef really buy us anything here?
>
> I guess it might save a *TINY* amount of time at alternative processing time. But
> that doesn't really seem worth it.

You have kept saying not to use #ifdef if possible, and I tried to get if of them.

Somehow I ended up with overlooking this _unnecessary_ change, will remove.

Thanks!
Xin