Messages in this thread | | | Date | Wed, 14 Feb 2018 20:06:29 +0100 | From | Dominik Brodowski <> | Subject | Re: [RFC PATCH 3/4] x86/entry/64: move switch_to_thread_stack to interrupt helper function |
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On Wed, Feb 14, 2018 at 01:57:15PM -0500, Brian Gerst wrote: > On Wed, Feb 14, 2018 at 1:21 PM, Dominik Brodowski > <linux@dominikbrodowski.net> wrote: > > We can also move the SWAPGS and the switch_to_thread_stack to the > > interrupt helper function. As we do not want call depths of two, > > convert switch_to_thread_stack to a macro. However, as entry_64_compat.S > > expects switch_to_thread_stack to be a function, provide a wrapper for > > that, which leads to some code duplication if CONFIG_IA32_EMULATION is > > enabled. Therefore, the size reduction differs slightly: > > > > With CONFIG_IA32_EMULATION enabled (-0.13k): > > text data bss dec hex filename > > 16897 0 0 16897 4201 entry_64.o-orig > > 16767 0 0 16767 417f entry_64.o > > > > With CONFIG_IA32_EMULATION disabled (-0.27k): > > text data bss dec hex filename > > 16897 0 0 16897 4201 entry_64.o-orig > > 16622 0 0 16622 40ee entry_64.o > > > > Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net> > > --- > > arch/x86/entry/entry_64.S | 65 ++++++++++++++++++++++++++--------------------- > > 1 file changed, 36 insertions(+), 29 deletions(-) > > > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > > index 3046b12a1acb..b60a3b692ca9 100644 > > --- a/arch/x86/entry/entry_64.S > > +++ b/arch/x86/entry/entry_64.S > > @@ -536,6 +536,31 @@ END(irq_entries_start) > > decl PER_CPU_VAR(irq_count) > > .endm > > > > +/* > > + * Switch to the thread stack. This is called with the IRET frame and > > + * orig_ax on the stack. (That is, RDI..R12 are not on the stack and > > + * space has not been allocated for them.) > > + */ > > +.macro DO_SWITCH_TO_THREAD_STACK > > + pushq %rdi > > + /* Need to switch before accessing the thread stack. */ > > + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi > > + movq %rsp, %rdi > > + movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp > > + UNWIND_HINT sp_offset=16 sp_reg=ORC_REG_DI > > + > > + pushq 7*8(%rdi) /* regs->ss */ > > + pushq 6*8(%rdi) /* regs->rsp */ > > + pushq 5*8(%rdi) /* regs->eflags */ > > + pushq 4*8(%rdi) /* regs->cs */ > > + pushq 3*8(%rdi) /* regs->ip */ > > + pushq 2*8(%rdi) /* regs->orig_ax */ > > + pushq 8(%rdi) /* return address */ > > + UNWIND_HINT_FUNC > > + > > + movq (%rdi), %rdi > > +.endm > > + > > /* > > * Interrupt entry/exit. > > * > > @@ -543,10 +568,17 @@ END(irq_entries_start) > > * > > * Entry runs with interrupts off. > > */ > > +/* 8(%rsp): ~(interrupt number) */ > > ENTRY(interrupt_helper) > > UNWIND_HINT_FUNC > > cld > > > > + testb $3, CS-ORIG_RAX+8(%rsp) > > + jz 1f > > + SWAPGS > > + DO_SWITCH_TO_THREAD_STACK > > +1: > > + > > PUSH_AND_CLEAR_REGS save_ret=1 > > ENCODE_FRAME_POINTER 8 > > > > @@ -579,12 +611,6 @@ END(interrupt_helper) > > .macro interrupt func > > cld > > > > - testb $3, CS-ORIG_RAX(%rsp) > > - jz 1f > > - SWAPGS > > - call switch_to_thread_stack > > -1: > > - > > call interrupt_helper > > > > call \func /* rdi points to pt_regs */ > > @@ -853,33 +879,14 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt > > */ > > #define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + ((x) - 1) * 8) > > > > -/* > > - * Switch to the thread stack. This is called with the IRET frame and > > - * orig_ax on the stack. (That is, RDI..R12 are not on the stack and > > - * space has not been allocated for them.) > > - */ > > +#if defined(CONFIG_IA32_EMULATION) > > +/* entry_64_compat.S::entry_INT80_compat expects this to be an ASM function */ > > ENTRY(switch_to_thread_stack) > > UNWIND_HINT_FUNC > > - > > - pushq %rdi > > - /* Need to switch before accessing the thread stack. */ > > - SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi > > - movq %rsp, %rdi > > - movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp > > - UNWIND_HINT sp_offset=16 sp_reg=ORC_REG_DI > > - > > - pushq 7*8(%rdi) /* regs->ss */ > > - pushq 6*8(%rdi) /* regs->rsp */ > > - pushq 5*8(%rdi) /* regs->eflags */ > > - pushq 4*8(%rdi) /* regs->cs */ > > - pushq 3*8(%rdi) /* regs->ip */ > > - pushq 2*8(%rdi) /* regs->orig_ax */ > > - pushq 8(%rdi) /* return address */ > > - UNWIND_HINT_FUNC > > - > > - movq (%rdi), %rdi > > + DO_SWITCH_TO_THREAD_STACK > > ret > > END(switch_to_thread_stack) > > +#endif > > > > .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 > > ENTRY(\sym) > > -- > > 2.16.1 > > > > Move the macro to calling.h, and inline it into the compat entry.
That certainly sounds possible, but makes the macro more complex: Inlining means that the offsets need to be reduced by -8. But we need the current offset for the call from interrupt_helper. So such a change might make the code less readable.
Thanks, Dominik
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