Commit 3304c9c3 authored by Denys Vlasenko's avatar Denys Vlasenko Committed by Ingo Molnar
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x86/asm/entry/irq: Simplify interrupt dispatch table (IDT) layout 



Interrupt entry points are handled with the following code,
each 32-byte code block contains seven entry points:

		...
		[push][jump 22] // 4 bytes
		[push][jump 18] // 4 bytes
		[push][jump 14] // 4 bytes
		[push][jump 10] // 4 bytes
		[push][jump  6] // 4 bytes
		[push][jump  2] // 4 bytes
		[push][jump common_interrupt][padding] // 8 bytes

		[push][jump]
		[push][jump]
		[push][jump]
		[push][jump]
		[push][jump]
		[push][jump]
		[push][jump common_interrupt][padding]

		[padding_2]
	common_interrupt:

And there is a table which holds pointers to every entry point,
IOW: to every push.

In cold cache, two jumps are still costlier than one, even
though we get the benefit of them residing in the same
cacheline.

This change replaces short jumps with near ones to
'common_interrupt', and pads every push+jump pair to 8 bytes. This
way, each interrupt takes only one jump.

This change replaces ".p2align CONFIG_X86_L1_CACHE_SHIFT" before
dispatch table with ".align 8" - we do not need anything
stronger than that.

The table of entry addresses (the interrupt[] array) is no
longer necessary, the address of entries can be easily
calculated as (irq_entries_start + i*8).

   text	   data	    bss	    dec	    hex	filename
  12546	      0	      0	  12546	   3102	entry_64.o.before
  11626	      0	      0	  11626	   2d6a	entry_64.o

The size decrease is because 1656 bytes of .init.rodata are
gone. That's initdata, though. The resident size does go up a
bit.

Run-tested (32 and 64 bits).

Acked-and-Tested-by: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarDenys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1428090553-7283-1-git-send-email-dvlasenk@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent fffbb5dc

arch/x86/include/asm/hw_irq.h

+2 −3
Original line number Diff line number Diff line
@@ -181,10 +181,9 @@ extern __visible void smp_call_function_single_interrupt(struct pt_regs *); 
extern __visible void smp_invalidate_interrupt(struct pt_regs *);

#endif



extern void (*__initconst interrupt[FIRST_SYSTEM_VECTOR

				    - FIRST_EXTERNAL_VECTOR])(void);

extern char irq_entries_start[];

#ifdef CONFIG_TRACING

#define trace_interrupt interrupt

#define trace_irq_entries_start irq_entries_start

#endif



#define VECTOR_UNDEFINED	(-1)

arch/x86/kernel/entry_32.S

+10 −31
Original line number Diff line number Diff line
@@ -723,43 +723,22 @@ END(sysenter_badsys) 
.endm



/*

 * Build the entry stubs and pointer table with some assembler magic.

 * We pack 7 stubs into a single 32-byte chunk, which will fit in a

 * single cache line on all modern x86 implementations.

 * Build the entry stubs with some assembler magic.

 * We pack 1 stub into every 8-byte block.

 */

.section .init.rodata,"a"

ENTRY(interrupt)

.section .entry.text, "ax"

	.p2align 5

	.p2align CONFIG_X86_L1_CACHE_SHIFT

	.align 8

ENTRY(irq_entries_start)

	RING0_INT_FRAME

    vector=FIRST_EXTERNAL_VECTOR

.rept (FIRST_SYSTEM_VECTOR-FIRST_EXTERNAL_VECTOR+6)/7

	.balign 32

  .rept	7

    .if vector < FIRST_SYSTEM_VECTOR

      .if vector <> FIRST_EXTERNAL_VECTOR

	CFI_ADJUST_CFA_OFFSET -4

      .endif

1:	pushl_cfi $(~vector+0x80)	/* Note: always in signed byte range */

      .if ((vector-FIRST_EXTERNAL_VECTOR)%7) <> 6

	jmp 2f

      .endif

      .previous

	.long 1b

      .section .entry.text, "ax"

    .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)

	pushl_cfi $(~vector+0x80)	/* Note: always in signed byte range */

    vector=vector+1

    .endif

  .endr

2:	jmp common_interrupt

	jmp	common_interrupt

	CFI_ADJUST_CFA_OFFSET -4

	.align	8

    .endr

END(irq_entries_start)



.previous

END(interrupt)

.previous



/*

 * the CPU automatically disables interrupts when executing an IRQ vector,

 * so IRQ-flags tracing has to follow that:

arch/x86/kernel/entry_64.S

+10 −31
Original line number Diff line number Diff line
@@ -608,44 +608,23 @@ ENTRY(ret_from_fork) 
END(ret_from_fork)



/*

 * Build the entry stubs and pointer table with some assembler magic.

 * We pack 7 stubs into a single 32-byte chunk, which will fit in a

 * single cache line on all modern x86 implementations.

 * Build the entry stubs with some assembler magic.

 * We pack 1 stub into every 8-byte block.

 */

	.section .init.rodata,"a"

ENTRY(interrupt)

	.section .entry.text

	.p2align 5

	.p2align CONFIG_X86_L1_CACHE_SHIFT

	.align 8

ENTRY(irq_entries_start)

	INTR_FRAME

    vector=FIRST_EXTERNAL_VECTOR

.rept (FIRST_SYSTEM_VECTOR-FIRST_EXTERNAL_VECTOR+6)/7

	.balign 32

  .rept	7

    .if vector < FIRST_SYSTEM_VECTOR

      .if vector <> FIRST_EXTERNAL_VECTOR

	CFI_ADJUST_CFA_OFFSET -8

      .endif

1:	pushq_cfi $(~vector+0x80)	/* Note: always in signed byte range */

      .if ((vector-FIRST_EXTERNAL_VECTOR)%7) <> 6

	jmp 2f

      .endif

      .previous

	.quad 1b

      .section .entry.text

    .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)

	pushq_cfi $(~vector+0x80)	/* Note: always in signed byte range */

    vector=vector+1

    .endif

  .endr

2:	jmp common_interrupt

	jmp	common_interrupt

	CFI_ADJUST_CFA_OFFSET -8

	.align	8

    .endr

	CFI_ENDPROC

END(irq_entries_start)



.previous

END(interrupt)

.previous



/*

 * Interrupt entry/exit.

 *

arch/x86/kernel/irqinit.c

+2 −1
Original line number Diff line number Diff line
@@ -178,7 +178,8 @@ void __init native_init_IRQ(void) 
#endif

	for_each_clear_bit_from(i, used_vectors, first_system_vector) {

		/* IA32_SYSCALL_VECTOR could be used in trap_init already. */

		set_intr_gate(i, interrupt[i - FIRST_EXTERNAL_VECTOR]);

		set_intr_gate(i, irq_entries_start +

				8 * (i - FIRST_EXTERNAL_VECTOR));

	}

#ifdef CONFIG_X86_LOCAL_APIC

	for_each_clear_bit_from(i, used_vectors, NR_VECTORS)

arch/x86/lguest/boot.c

+2 −1
Original line number Diff line number Diff line
@@ -868,7 +868,8 @@ static void __init lguest_init_IRQ(void) 
		/* Some systems map "vectors" to interrupts weirdly.  Not us! */

		__this_cpu_write(vector_irq[i], i - FIRST_EXTERNAL_VECTOR);

		if (i != SYSCALL_VECTOR)

			set_intr_gate(i, interrupt[i - FIRST_EXTERNAL_VECTOR]);

			set_intr_gate(i, irq_entries_start +

					8 * (i - FIRST_EXTERNAL_VECTOR));

	}



	/*

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