Re: [PATCH 02/11] Add "handle page fault" PV helper.

From: Avi Kivity
Date: Mon Nov 02 2009 - 23:57:34 EST

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 | â | (Intel reserved. Do not use.) | | No |
20-31 | â | Intel reserved. Do not use. |
32-255 | â | 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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