Re: [RFC PATCH 3/4] x86/entry/64: move switch_to_thread_stack to interrupt helper function

From: Brian Gerst
Date: Wed Feb 14 2018 - 13:57:23 EST


On Wed, Feb 14, 2018 at 1:21 PM, Dominik Brodowski
<linux@xxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxx>
> ---
> 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.

--
Brian Gerst