[Xen-devel] Passing pointers to hypercalls

["Amaro, Emmanuel" <amaro@xxxxxxxxxx>]

Hello,

I am trying to pass a pointer to an hyper call in the simplest possible way, set itâs value, an return it to the guest.

I have tried 2 different ways:

- Directly with simple pointers (I read somewhere this would work on x86), but the pointer address is set to 0x0000deadbeef, so dereferencing it causes a panic.

- With XEN_GUEST_HANDLE:

long do_dummy(XEN_GUEST_HANDLE(uint64_t) ptr)

{

    uint64_t tmp = 1;

    if (copy_to_guest(ptr, &tmp, 1) != 0)

        return 2;

    return 0;

}

But in this case copy_to_guest() does not return 0, so this fails as well. I call the hyper call from this Linux system call:

asmlinkage long sys_dummy(void)

{

    uint64_t p = 0;

    int rc = 0;

    rc = HYPERVISOR_dummy(&p);

    if (rc != 0)

        printk("ERROR, hypercall returned: %d\n", rc);

    return 0;

}

I am sure I am missing something super easy, but I canât see what.

Thank you for your help,

Emmanuel

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