Re: 5 gigs of contiguos kernel VM shared with userspace

[snip]

I .. thought? that technically speaking the kernel virtual address
space and userland virtual address
space are (a) not the same, and (b) user VA in the past wasn't even
guaranteed to be visible by the kernel.

I know on 64 bit platforms people .. bend the rules / make
optimisation assumptions like this.

Are you looking for the /same/ virtual addresses in kernel versus
userland? Or just some guarantee
that for a given range of kernel virtual addresses, it's linearly
mapped in the same linear order to a
userland process? (ie, knowing the start of the UVA / KVA in their
respective running modes is enough;
everything else is just an offset to that.)

Because if /that/ is OK, then you can do that with the pager interface
markj@ is saying and this is how
a lot of stuff gets exposed between userland/kernel.

If you're looking for other more funkier stuff (eg you're involving
RDMA, GPU vtable /NIC vtable / system
IOMMU shenanigans) then maybe explain it a bit more?



-adrian