On Sun, Nov 22, 2009 at 4:01 AM, Segher Boessenkool
[off-list ref] wrote:

quoted

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You need to be a bit more careful tho. You must not allow RAM managed b=

y

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the kernel to be mapped non-cachable.

Even if the user explicitly sets the O_SYNC flag? =C2=A0IMHO, it's a bug=

 of

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the application if it uses O_SYNC on main memory to be mmap'ed later.
And we don't need to cover up the bug.

Is that "embedded thinking"? =C2=A0Conflicts like this cause machine chec=

ks or

checkstops on many PowerPC implementations, we do not normally allow such
to be caused by userland.

So what you are saying is that if the kernel has mapped a physical
page as cacheable while user application is trying to map it as
non-cacheable, there will be machine checks and checkstops rather than
just performance drop?  This is new to me.  Could you elaborate a bit?
 Thanks.

- Leo