> -----Original Message----- > From: Li, Xin3 <xin3.li@xxxxxxxxx> > Sent: Monday, April 10, 2023 11:32 AM > To: Hansen, Dave <dave.hansen@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; > x86@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx > Cc: tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; bp@xxxxxxxxx; > dave.hansen@xxxxxxxxxxxxxxx; hpa@xxxxxxxxx; peterz@xxxxxxxxxxxxx; > andrew.cooper3@xxxxxxxxxx; Christopherson,, Sean <seanjc@xxxxxxxxxx>; > pbonzini@xxxxxxxxxx; Shankar, Ravi V <ravi.v.shankar@xxxxxxxxx>; > jiangshanlai@xxxxxxxxx; Kang, Shan <shan.kang@xxxxxxxxx> > Subject: RE: [PATCH v7 23/33] x86/fred: let ret_from_fork() jmp to fred_exit_user > when FRED is enabled > > > 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. Actually I didn't overlook it, the reason I keep the #ifdef is the symbol "fred_exit_user" is missing otherwise, which is defined only if we have CONFIG_X86_FRED. Thanks! Xin
