[Xen-devel] Re: [RFC PATCH 23/35] Increase x86 interrupt vector range

[Chuck Ebbert <76306.1226@xxxxxxxxxxxxxx>]

In-Reply-To: <20060509085157.070289000@xxxxxxxxxxxx>

On Tue, 09 May 2006 00:00:23 -0700, Chris Wright wrote:


> Remove the limit of 256 interrupt vectors by changing the value
> stored in orig_{e,r}ax to be the negated 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@xxxxxxxxxxxxx>
> Signed-off-by: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
> Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
> ---

AFAIC this could go in anytime.  It's simple, self-contained and makes
sense even without Xen.

One minor nit: the IRQ value isn't negated, it's complemented.  The
comments need to be fixed.

Original patch:

 arch/i386/kernel/entry.S    |    4 ++--
 arch/i386/kernel/irq.c      |    4 ++--
 arch/x86_64/kernel/entry.S  |    2 +-
 arch/x86_64/kernel/irq.c    |    4 ++--
 arch/x86_64/kernel/smp.c    |    4 ++--
 include/asm-x86_64/hw_irq.h |    2 +-
 6 files changed, 10 insertions(+), 10 deletions(-)

--- linus-2.6.orig/arch/i386/kernel/entry.S
+++ linus-2.6/arch/i386/kernel/entry.S
@@ -464,7 +464,7 @@ vector=0
 ENTRY(irq_entries_start)
 .rept NR_IRQS
        ALIGN
-1:     pushl $vector-256
+1:     pushl $~(vector)
        jmp common_interrupt
 .data
        .long 1b
@@ -481,7 +481,7 @@ common_interrupt:
 
 #define BUILD_INTERRUPT(name, nr)      \
 ENTRY(name)                            \
-       pushl $nr-256;                  \
+       pushl $~(nr);                   \
        SAVE_ALL                        \
        movl %esp,%eax;                 \
        call smp_/**/name;              \
--- linus-2.6.orig/arch/i386/kernel/irq.c
+++ linus-2.6/arch/i386/kernel/irq.c
@@ -53,8 +53,8 @@ static union irq_ctx *softirq_ctx[NR_CPU
  */
 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;
--- linus-2.6.orig/arch/x86_64/kernel/entry.S
+++ linus-2.6/arch/x86_64/kernel/entry.S
@@ -601,7 +601,7 @@ retint_kernel:      
  */            
        .macro apicinterrupt num,func
        INTR_FRAME
-       pushq $\num-256
+       pushq $~(\num)
        CFI_ADJUST_CFA_OFFSET 8
        interrupt \func
        jmp ret_from_intr
--- linus-2.6.orig/arch/x86_64/kernel/irq.c
+++ linus-2.6/arch/x86_64/kernel/irq.c
@@ -91,8 +91,8 @@ skip:
  */
 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();
--- linus-2.6.orig/arch/x86_64/kernel/smp.c
+++ linus-2.6/arch/x86_64/kernel/smp.c
@@ -135,10 +135,10 @@ asmlinkage void smp_invalidate_interrupt
 
        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))
--- linus-2.6.orig/include/asm-x86_64/hw_irq.h
+++ linus-2.6/include/asm-x86_64/hw_irq.h
@@ -127,7 +127,7 @@ 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)

-- 
Chuck

"The x86 isn't all that complex -- it just doesn't make a lot of sense."
                                                        -- Mike Johnson

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