[PATCH] x86: increase interrupt vector range

Remove the limit of 256 interrupt vectors by changing the value stored in
orig_{e,r}ax to be the complemented interrupt vector.  The orig_{e,r}ax
needs to be < 0 to allow the signal code to distinguish between return from
interrupt and return from syscall.  With this change applied, NR_IRQS can
be > 256.

Xen extends the IRQ numbering space to include room for dynamically
allocated virtual interrupts (in the range 256-511), which requires a more
permissive interface to do_IRQ.
Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Protasevich, Natalie" <Natalie.Protasevich@UNISYS.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/entry.S

@@ -515,7 +515,7 @@ ENTRY(irq_entries_start)
  .if vector
 	CFI_ADJUST_CFA_OFFSET -4
  .endif
-1:	pushl $vector-256
+1:	pushl $~(vector)
 	CFI_ADJUST_CFA_OFFSET 4
 	jmp common_interrupt
 .data
@@ -535,7 +535,7 @@ common_interrupt:
 #define BUILD_INTERRUPT(name, nr)	\
 ENTRY(name)				\
 	RING0_INT_FRAME;		\
-	pushl $nr-256;			\
+	pushl $~(nr);			\
 	CFI_ADJUST_CFA_OFFSET 4;	\
 	SAVE_ALL;			\
 	movl %esp,%eax;			\

arch/i386/kernel/irq.c

@@ -53,8 +53,8 @@ static union irq_ctx *softirq_ctx[NR_CPUS] __read_mostly;
  */
 fastcall unsigned int do_IRQ(struct pt_regs *regs)
 {	
-	/* high bits used in ret_from_ code */
-	int irq = regs->orig_eax & 0xff;
+	/* high bit used in ret_from_ code */
+	int irq = ~regs->orig_eax;
 #ifdef CONFIG_4KSTACKS
 	union irq_ctx *curctx, *irqctx;
 	u32 *isp;

arch/x86_64/kernel/entry.S

@@ -588,7 +588,7 @@ END(common_interrupt)
  */		
 	.macro apicinterrupt num,func
 	INTR_FRAME
-	pushq $\num-256
+	pushq $~(\num)
 	CFI_ADJUST_CFA_OFFSET 8
 	interrupt \func
 	jmp ret_from_intr

arch/x86_64/kernel/irq.c

@@ -115,8 +115,8 @@ int show_interrupts(struct seq_file *p, void *v)
  */
 asmlinkage unsigned int do_IRQ(struct pt_regs *regs)
 {	
-	/* high bits used in ret_from_ code  */
-	unsigned irq = regs->orig_rax & 0xff;
+	/* high bit used in ret_from_ code  */
+	unsigned irq = ~regs->orig_rax;
 
 	exit_idle();
 	irq_enter();

arch/x86_64/kernel/smp.c

@@ -135,10 +135,10 @@ asmlinkage void smp_invalidate_interrupt(struct pt_regs *regs)
 
 	cpu = smp_processor_id();
 	/*
-	 * orig_rax contains the interrupt vector - 256.
+	 * orig_rax contains the negated interrupt vector.
 	 * Use that to determine where the sender put the data.
 	 */
-	sender = regs->orig_rax + 256 - INVALIDATE_TLB_VECTOR_START;
+	sender = ~regs->orig_rax - INVALIDATE_TLB_VECTOR_START;
 	f = &per_cpu(flush_state, sender);
 
 	if (!cpu_isset(cpu, f->flush_cpumask))

include/asm-x86_64/hw_irq.h

@@ -124,7 +124,7 @@ asmlinkage void IRQ_NAME(nr); \
 __asm__( \
 "\n.p2align\n" \
 "IRQ" #nr "_interrupt:\n\t" \
-	"push $" #nr "-256 ; " \
+	"push $~(" #nr ") ; " \
 	"jmp common_interrupt");
 
 #if defined(CONFIG_X86_IO_APIC)