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SubjectRe: Subject: [PATCH 1/2] x86: get back 15 vectors
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Yinghai Lu <yinghai@kernel.org> writes:

> On 01/04/2010 11:48 AM, H. Peter Anvin wrote:
>> [Adding Suresh to the Cc: list]
>>
>> On 01/04/2010 11:35 AM, Yinghai Lu wrote:
>>>
>>> so we can use [0x10, 0x1f]
>>>
>>> sth like this?
>>>
>>
>> No!!!
>>
>> [0x10, 0x1f] is reserved for exceptions. We can probably get away with
>> stealing *one* vector... presumably at the end (0x1f). However, we can
>> absolutely not use the whole block: 0x10-0x13 is occupied by exceptions
>> we already have OS support for (#MF, #AC, #MC, and #XM), and it's pretty
>> much guaranteed we'll have more coming. However, growth is quite slow
>> and since this is a kernel-internal vector (not accessible to user
>> space) it is not creating an API.
>>
>> In other words, we could change FIRST_EXTERNAL_VECTOR to 0x1f, and use
>> it for IRQ_MOVE_CLEANUP_VECTOR. Then use 0x20..0x2f for the legacy vectors.
>>
> Subject: [PATCH 1/2] x86: get back 16 vectors
>
> -v2: according to hpa that we could start from 0x1f

The code in the patch is ok, but the comments are wrong.

>
> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
>
> ---
> arch/x86/include/asm/irq_vectors.h | 9 +++++----
> 1 file changed, 5 insertions(+), 4 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
> @@ -30,8 +30,9 @@
> /*
> * IDT vectors usable for external interrupt sources start
> * at 0x20:
> + * hpa said we can start from 0x1f

You need to document the reasons here.

> */
> -#define FIRST_EXTERNAL_VECTOR 0x20
> +#define FIRST_EXTERNAL_VECTOR 0x1f
>
> #ifdef CONFIG_X86_32
> # define SYSCALL_VECTOR 0x80
> @@ -41,15 +42,15 @@
> #endif
>
> /*
> - * Reserve the lowest usable priority level 0x20 - 0x2f for triggering
> + * Reserve the lowest usable priority level 0x1f for triggering

Should be:
+ * 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.
> */
> -#define IRQ0_VECTOR (FIRST_EXTERNAL_VECTOR + 0x10)
> +#define IRQ0_VECTOR (FIRST_EXTERNAL_VECTOR + 1)
>
> #define IRQ1_VECTOR (IRQ0_VECTOR + 1)
> #define IRQ2_VECTOR (IRQ0_VECTOR + 2)


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