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SubjectRe: FOR REVIEW: New x86-64 vsyscall vgetcpu()
Andi Kleen wrote:

> That is not how user space TLS works. It usually has a base a register.

Can you please give me a real life (simplified) example?

> This means it cannot be cache colored (because you would need a static
> offset) and you couldn't share task_structs on a page.

I do not see the problem. Can you explain please?
E.g. the scheduler pulls a task instead of the current one. The CPU
will see "current->thread_info.cpu"-s of all the tasks at the same
offset anyway.

> Also you would make task_struct part of the userland ABI which
> seems like a very very bad idea to me. It means we couldn't change
> it anymore.

We can make some wrapper, e.g.:

user_per_cpu_var(name, offset)

"vgetcpu()" would also be added to the ABI which we couldn't change
easily either.


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