Re: [PATCH] i386 uaccess to fixmap pages

[Linus Torvalds]

On Fri, 9 May 2003, Dave Hansen wrote:
> 
> We've been playing with patches in the -mjb tree which make PAGE_OFFSET
> and TASK_SIZE move to some weird values.  I have it to the point where I
> could do a 3.875:0.125 user:kernel split.

That's still not "weird" in the current sense.

We've always (well, for a long time) been able to handle a TASK_SIZE that 
has a 111..00000 pattern - and in fact we used to _depend_ on that kind of 
pattern, because macros like "virt_to_phys()" were simple bitwise-and 
operations. There may be some code in the kernel that still depends on 
that kind of bitwise operation with TASK_SIZE.

Your 3.875:0.125 split still fits that pattern, and thus doesn't create 
any new cases.

In contrast, a TASK_SIZE of 0xc1000000 can no longer just "mask off" the 
kernel address bits. And _that_ is what I meant with "strange value".

		Linus