[tip:x86/asm] x86/asm/entry/irq: Simplify interrupt dispatch table (IDT) layout

From: tip-bot for Denys Vlasenko
Date: Wed Apr 08 2015 - 03:44:21 EST

Commit-ID: 3304c9c37bef30ebd2ef71d986e6568372ce80f8
Gitweb: http://git.kernel.org/tip/3304c9c37bef30ebd2ef71d986e6568372ce80f8
Author: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
AuthorDate: Fri, 3 Apr 2015 21:49:13 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 8 Apr 2015 09:02:13 +0200

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: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Will Drewry <wad@xxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1428090553-7283-1-git-send-email-dvlasenk@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/include/asm/hw_irq.h | 5 ++---
arch/x86/kernel/entry_32.S | 41 ++++++++++-------------------------------
arch/x86/kernel/entry_64.S | 41 ++++++++++-------------------------------
arch/x86/kernel/irqinit.c | 3 ++-
arch/x86/lguest/boot.c | 3 ++-
5 files changed, 26 insertions(+), 67 deletions(-)

diff --git a/arch/x86/include/asm/hw_irq.h b/arch/x86/include/asm/hw_irq.h
index 9662290..e9571dd 100644
--- a/arch/x86/include/asm/hw_irq.h
+++ b/arch/x86/include/asm/hw_irq.h
@@ -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)
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index effa279..02bec0f 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -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
+ vector=FIRST_EXTERNAL_VECTOR
+ .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
+ pushl_cfi $(~vector+0x80) /* Note: always in signed byte range */
+ vector=vector+1
+ jmp common_interrupt
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"
-vector=vector+1
- .endif
- .endr
-2: jmp common_interrupt
-.endr
+ .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:
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e4c8103..4ca03c5 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -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
+ vector=FIRST_EXTERNAL_VECTOR
+ .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
+ pushq_cfi $(~vector+0x80) /* Note: always in signed byte range */
+ vector=vector+1
+ jmp common_interrupt
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
-vector=vector+1
- .endif
- .endr
-2: jmp common_interrupt
-.endr
+ .align 8
+ .endr
CFI_ENDPROC
END(irq_entries_start)

-.previous
-END(interrupt)
-.previous
-
/*
* Interrupt entry/exit.
*
diff --git a/arch/x86/kernel/irqinit.c b/arch/x86/kernel/irqinit.c
index 70e181e..cd10a64 100644
--- a/arch/x86/kernel/irqinit.c
+++ b/arch/x86/kernel/irqinit.c
@@ -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)
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 8561585..717908b 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -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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