On Sunday 08 April 2001 10:28, Lothar Krause wrote:
> Is there some way to get a shared memory area that has the same address in
> both kernel and user space?
AFAIK, kernel space normally maps it's memory in the high end of the 4 GB
range (on x86), precisely in order to *avoid* collisions with user space
mappings. (That way, you can avoid some linear->physic translation table
swapping when entering kernel space; the mappnigs are always there, but just
not accessible from user space.)
I think it should theoretically possible to map almost any physical memory to
any free region, whether in kernel space or in user space, but I can't see
how it could be done with less than reserving a part of the linear address
space globally. (If *any* task could replace that mapping, you'd be in
trouble when the RTL thread tries to access the shared area...)
It doesn't seem like a thing that would be explicitly supported, but there
might be some shortcut.
Changing the access flags on memory pages allocated from the kernel heap
could work, I guess, but without some further hacking (changing those pages
upon switches between tasks with access and other tasks), it would mean that
*any* task gets access to the memory. Major security hole. :-)
//David
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