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@suse.de> Signed-off-by: Denys 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: Ingo Molnar <mingo@kernel.org>
2015-04-03 21:49:13 +02:00 · 2015-04-03 21:49:13 +02:00 · 3304c9c37b
parent fffbb5dcfd
commit 3304c9c37b
5 changed files with 26 additions and 67 deletions
--- 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)
--- 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:
--- 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.
 *
--- 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)
--- 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));
 	}

 	/*