linux-kernel - linux PowerPC 85xx Address space query

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Date:	Wed, 24 Jun 2009 16:15:41 +0530
From:	kernel mailz <kernelmailz@...glemail.com>
To:	linux-kernel@...r.kernel.org
Subject: linux PowerPC 85xx Address space query

Hi,

I am a newbie, trying to learn but have a few queries, nice if you could respond
For linux on 85xx systems...

(a) Kernel code runs in PR=0 AS=0 and PID=0, which user space
application run in PR=1 AS=0 and PID 1-255.
Is this correct.

(b) I am writing a small program where the application code opens
invokes a ioctl call and passes a buffer pointer ( say 0x10000 in user
space)
Now the driver code is using copy_from_user.
How this works internally ?

1. User code executes ioctl
2. interrupt goes to the kernel
3. ioctl handler in driver gets invoked
The buffer pointer still contains 0x10000.

How kernel code running in PR=0 accesses it and does the copy. I am
not able to see a address space switch in the asm code of
copy_tofrom_user.

Please respond

-TRX
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