Re: [Xen-users] use hypercall in kernel module

[Julien Grall <julien.grall@xxxxxxx>]

Hello,

On 25/05/16 04:47, Big Strong wrote:
> While we can use privcmd_call in hypercall.h to issue the hypercall in
> kernel module, it is unclear how to set the arguments to adapt it to
> registers.
>
>
>     static inline long privcmd_call(unsigned call,
>               unsigned long a1, unsigned long a2,
>               unsigned long a3, unsigned long a4,
>               unsigned long a5)
>     {
>          __HYPERCALL_DECLS;
>          __HYPERCALL_5ARG(a1, a2, a3, a4, a5);
>          asm volatile("call *%[call]"
>                   : __HYPERCALL_5PARAM
>                   : [call] "a" (&*hypercall_page*[call])
>                   : __HYPERCALL_CLOBBER5);
>          return (long)__res;
>     }
>
>
> Take HYPERCALL_hvm_op as an example, the arguments are op and arg, when
> the op is HVMOP_altp2m, we need to convert arg to xen_hvm_altp2m_op. Now
> what if I want to directly assign a xen_hvm_altp2m_op as the argument a2
> and HVMOP_altp2m as a1 and __HYPERVISOR_hvm_op as call? How can a2 be
> assigned as it is defined as a uint64 while xen_hvm_altp2m_op is a
> structure? Should I use (xen_hvm_altp2m_op *) pointer as a2?
>
> Or is there any example on how to use hypercall in LKM (linux loadable
> kernel module)? I don't know how to convert the arguments to registers.
Give a look to arch/x86/asm/xen/hypercall.h to see how hypercalls are 
implemented for the kernel.
Regards,

--
Julien Grall

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