Re: double fault -> PAGE_KERNEL flagged memory

[Mathieu Desnoyers <compudj@krystal.dyndns.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


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