Subject: Re: Subject: [PATCH 1/2] x86: get back 15 vectors

From: Yinghai Lu <[email-masked]>
Date: Mon, 04 Jan 2010 16:16:06 -0800

On 01/04/2010 04:05 PM, Suresh Siddha wrote:
> On Mon, 2010-01-04 at 11:50 -0800, H. Peter Anvin wrote:
>> On 01/04/2010 11:45 AM, Suresh Siddha wrote:
>>> On Mon, 2010-01-04 at 11:35 -0800, Yinghai Lu wrote:
>>>> sth like this?
>>>>
>>>> Subject: [PATCH 1/2] x86: get back 16 vectors
>>>>
>>>> -v2: according to hpa that we could start from 0x10
>>>>      according to Eric, we should hold 16 vectors for IRQ MOVE
>>>>
>>>> Signed-off-by: Yinghai Lu <[email-masked]>
>>>>
>>>
>>> Yinghai we have to change IRQ_MOVE_CLEANUP_VECTOR to 0x1f or so. From
>>> the cpu perspective this vector is documented as illegal, so we need to
>>> check if this change will work on the cpu's we have today to get some
>>> confidence.
>>>
>>
>> It's documented as reserved, not illegal.  The ability for the APIC to
>> generate vectors starting at 0x10 is documented, as is the ability for
>> the CPU to receive any vector number as an interrupt -- in fact, the
>> legacy BIOS relies on being able to receive interrupts starting at
>> vector 0x08.  It causes problems galore, but only at the software level.
> 
> I have checked out couple of platforms (including 32-bit atom) and 0x1f
> vector logic seems to be working.
> 
> Hopefully we won't have other hardware or software issues (vmm
> restrictions etc) with this logic.
> 

good. hope it is final version. let's have hpa own it.

From: "H. Peter Anvin" <[email-masked]>
Subject: [PATCH] x86: get back 16 vectors

-v2: according to hpa that we could start from 0x1f
-v3: update comments from Eric
-v4: update comments from hpa
-v5: use round up for IRQ0_VECTOR according to hpa

Signed-off-by: Yinghai Lu <[email-masked]>

---
 arch/x86/include/asm/irq_vectors.h |   40 ++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 14 deletions(-)

Index: linux-2.6/arch/x86/include/asm/irq_vectors.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/irq_vectors.h
+++ linux-2.6/arch/x86/include/asm/irq_vectors.h
@@ -30,26 +30,38 @@
 /*
  * IDT vectors usable for external interrupt sources start
  * at 0x20:
+ * hpa said we can start from 0x1f.
+ *   0x1f is documented as reserved.  However, the ability for the APIC
+ *   to generate vectors starting at 0x10 is documented, as is the
+ *   ability for the CPU to receive any vector number as an interrupt.
+ *   0x1f is used for IRQ_MOVE_CLEANUP_VECTOR since that vector needs
+ *   an entire privilege level (16 vectors) all by itself at a higher
+ *   priority than any actual device vector.  Thus, by placing it in the
+ *   otherwise-unusable 0x10 privilege level, we avoid wasting a full
+ *   16-vector block.
  */
-#define FIRST_EXTERNAL_VECTOR		0x20
+#define FIRST_EXTERNAL_VECTOR		0x1f
 
+#define IA32_SYSCALL_VECTOR		0x80
 #ifdef CONFIG_X86_32
 # define SYSCALL_VECTOR			0x80
-# define IA32_SYSCALL_VECTOR		0x80
-#else
-# define IA32_SYSCALL_VECTOR		0x80
 #endif
 
 /*
- * Reserve the lowest usable priority level 0x20 - 0x2f for triggering
+ * Reserve the lowest usable priority level 0x10 - 0x1f for triggering
  * cleanup after irq migration.
+ * this overlaps with the reserved range for cpu exceptions so this
+ * will need to be changed to 0x20 - 0x2f if the last cpu exception is
+ * ever allocated.
  */
+
 #define IRQ_MOVE_CLEANUP_VECTOR		FIRST_EXTERNAL_VECTOR
 
 /*
- * Vectors 0x30-0x3f are used for ISA interrupts.
+ * Vectors 0x20-0x2f are used for ISA interrupts.
+ *   round up to the next 16-vector boundary
  */
-#define IRQ0_VECTOR			(FIRST_EXTERNAL_VECTOR + 0x10)
+#define IRQ0_VECTOR			((FIRST_EXTERNAL_VECTOR + 16) & ~15)
 
 #define IRQ1_VECTOR			(IRQ0_VECTOR +  1)
 #define IRQ2_VECTOR			(IRQ0_VECTOR +  2)