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DateTue, 03 Nov 2009 06:57:07 +0200
FromAvi Kivity <>
SubjectRe: [PATCH 02/11] Add "handle page fault" PV helper.
On 11/03/2009 01:35 AM, Rik van Riel wrote:
>> We can't add an exception vector since all the existing ones are either
>> taken or reserved.
>
>
> I believe some are reserved for operating system use.

Table 6-1 says:

9 | | Coprocessor Segment Overrun (reserved) | Fault | No |
Floating-point instruction.2
15 | — | (Intel reserved. Do not use.) | | No |
20-31 | — | Intel reserved. Do not use. |
32-255 | — | User Defined (Non-reserved) Interrupts | Interrupt
| | External interrupt or INT n instruction.
So we can only use 32-255, but these are not fault-like exceptions that
can be delivered with interrupts disabled.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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