[v7,23/33] x86/fred: let ret_from_fork() jmp to fred_exit_user when FRED is enabled
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From: Xin Li <xin3.li@intel.com>
To: linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org
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Subject: [PATCH v7 23/33] x86/fred: let ret_from_fork() jmp to fred_exit_user
when FRED is enabled
Date: Tue, 4 Apr 2023 03:27:06 -0700
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| Series |
x86: enable FRED for x86-64
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Commit Message
Li, Xin3
April 4, 2023, 10:27 a.m. UTC
From: "H. Peter Anvin (Intel)" <hpa@zytor.com> Let ret_from_fork() jmp to fred_exit_user when FRED is enabled, otherwise the existing IDT code is chosen. Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com> Tested-by: Shan Kang <shan.kang@intel.com> Signed-off-by: Xin Li <xin3.li@intel.com> --- arch/x86/entry/entry_64.S | 5 +++++ 1 file changed, 5 insertions(+)
Comments
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.
> 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
> -----Original Message----- > From: Li, Xin3 <xin3.li@intel.com> > Sent: Monday, April 10, 2023 11:32 AM > To: Hansen, Dave <dave.hansen@intel.com>; linux-kernel@vger.kernel.org; > x86@kernel.org; kvm@vger.kernel.org > Cc: tglx@linutronix.de; mingo@redhat.com; bp@alien8.de; > dave.hansen@linux.intel.com; hpa@zytor.com; peterz@infradead.org; > andrew.cooper3@citrix.com; Christopherson,, Sean <seanjc@google.com>; > pbonzini@redhat.com; Shankar, Ravi V <ravi.v.shankar@intel.com>; > jiangshanlai@gmail.com; Kang, Shan <shan.kang@intel.com> > 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
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index eccc3431e515..5b595a9b2ffb 100644 --- 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 1: /* kernel thread */