Re: double fault -> PAGE_KERNEL flagged memory

[Mathieu Desnoyers <compudj at krystal dot dyndns dot org>]

* Mathieu Desnoyers (compudj@krystal.dyndns.org) wrote:

(talking about causes of a double fault in a Linux Kernel)

[...]
> 
> The same could apply to unaligned memory access.
> 
[...]

Sorry to reply to myself, but this isn't true in the Linux Kernel. The CPU
EFLAG Alignment Check is never activated in the Linux Kernel code. Furthermore,
alignment check exceptions never generate a double fault, as they are "benign
exceptions".

It still apply to page faults :

(from IA32 Intel Architecture Software Developer's Manual p. 6-14 vol.1)

#DF Double Fault

Source :

Any instruction that can generate an exception, an NMI or an INTR.

Well, not "any". For details, see table at vol. 3, p 5-38, same reference. In
fact, NMI and INTR seems to never generate a double fault.

Causes of a double fault :

Divide error, invalid TSS, segment not present, stack fault, general protection
nested on a page fault.

Page fault nested on another page fault.

Divide error, invalid TSS, segment not present, stack fault, general protection
nested on
divide error, invalid TSS, segment not present, stack fault, general protection.

In the other cases, the exceptions are handled serially.


Mathieu


OpenPGP public key:              http://krystal.dyndns.org:8080/key/compudj.gpg
Key fingerprint:     8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68