Re: [Xen-devel] disabling of X86_CR4_DE

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 09.01.06 18:13:43 >>>
>
>On 9 Jan 2006, at 16:06, Jan Beulich wrote:
>
>> Is there a particular reason for doing this unconditionally on both
32-
>> and 64-bits in xenolinux? It would seem to me that this feature
should
>> be disabled at most in unprivileged kernels... Thanks, Jan
>
>How do you mean? Looking at xen-unstable, we clear CR4_DE at the same

>point as native linux (i.e., we haven't changed code relating to that

>control flag at all).

I don't mean the cr4 modification; I rather referred to the feature
flag, which gets cleared in setup_arch_post.h's
machine_specific_modify_cpu_capabilities().

>It's not a debug-feature-enable flag anyway -- more a 
>backwards-compatibility flag for accesses to defunct debug registers 
>dr4 and dr5. It's pretty unimportant.

Not really. Its important function is to allow I/O port breakpoints.
(And I think disallowing access to dr4/dr5 isn't a bad thing, too.)

Jan

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