[LITMUS^RT] RFC control page & test suite fixes

[Andrea Bastoni]

On 06/27/2012 08:35 AM, Björn Brandenburg wrote:
> 
> On Jun 26, 2012, at 7:33 PM, Christopher Kenna wrote:
> 
>> On Mon, Jun 25, 2012 at 8:58 AM, Björn Brandenburg <bbb at mpi-sws.org> wrote:
>>>
>>> For the kernel, I've pushed prop/control-page-fixes, which improves the control page driver (but does not change the existing features).
>>>
>>> Please let me know if you have any comments.
>>
>> One question: Is __S011 more consistent across architectures (and
>> maybe PAGE_SHARED is not)? I thought they were equivalent but did not
>> dig deeply into the source for all architectures.
> 
> Good point, I wasn't sure about this. A quick search reveals that PAGE_SHARED is defined by most (all?) architectures, but that it is not used in architecture-indepdendent code (couldn't find it anywhere in include/, kernel/, mm/, net/, ipc/, or fs/). In contrast, __S011 is used in mm/mmap.c, so it has to be defined by all architectures. So I went with __S011.

Yep. I checked a bit, and it seems that the idea of PAGE_SHARED (NX,r/w) is not
the same across different architectures. For example, on microblaze or motorola
m68k, even if you'd like to have a 011 page, you end up with an executable page...

> Do you know of a place that documents which constants the VM subsystem expects to be defined by each architecture?

I believe the VM subsystem does not expect anything from architectures. My take
is that the protection_table in mm/mmap.c just lists the desired access
permissions, while the architecture layer maps those permissions on the
appropriate (and available) PAGE settings. Some architectures (e.g., x86) can do
that at compile time, while others (e.g., sparc) overwrite the protection_table
with the appropriate settings at runtime during the initialization of caches.

>> Also, your umlaut caused arch/x86/include/asm/feather_trace_32.h and
>> arch/x86/include/asm/feather_trace_64.h to flip to UTF-8 now. This is
>> probably not an issue though, correct?
> 
> Ooops. I think it should be ok since it's only in a comment. If it causes problem, let me know and I'll revert it.

These are on staging, right, not on control-page-fixes... I thought I was
missing something ;) UTF-8 should not be an issue anyway...

The patches look good to me!

Thanks,
- Andrea