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    SubjectRe: [uml-devel] new virtualization syscall to improve uml performance?

    It sounds like there are a couple of good ideas here. Let me add my

    new_addr(); /* to get a secondary address space */
    struct sandbox_params {
    int return_reason;
    int return_data;
    int eax;
    int ebx;
    run_sandbox(int address_space, struct sandbox_params *params); /* to start a sandbox */

    int fmmap(int address_space, void *start, size_t length, int prot,
    int flags, int fd, off_t offset);
    int fmunmap(int addresss_space, void *start, size_t length);

    With the secondary address spaces being completely setup by uml.
    And run_sandbox being the entry/exit point. The nice thing here is
    that because they would share the same kernel stack/process most
    registers can be left in registers. With run_sandbox putting as much
    as possible on a fast path.

    And then new_addr, fmmap, fmunmap would be all that you would really
    need to manipulate those address spaces.

    Usually processors only support a kernel/user space differentiation in
    their page tables, and the sometimes support caching multiple address
    spaces simultaneously cached in their tlbs. So I have designed this
    interface to take advantage of the common processor features, and
    additionally look as much like normal process execution as possible.
    Any other implementation would need someone manually modify the page
    tables, either the kernel or uml calling mprotect.

    Any trap taken in the sandboxed address space should fill the
    appropriate fields in struct sandbox_params and switch address spaces
    back to the master process.

    This interface is as cheap as I can imagine making it. And with
    a little care can be really optimized on the kernel side if uml
    becomes a common case.


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