size of hypercall parameter

size of hypercall parameter

[Anh Dinh]

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I wrote a hypercall that takes in a pointer to memory region:

void do_test(char *p){
... // do something with the memory in the hypervisor space
}

and invoke it in both Dom0 and DomU through privcmd.

But when I pass a memory region of tens of KB (not very large), the system
crashes and reboots.

Is there a limit to the memory region passed into the hypercall?

Cheers,
Anh.

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Re: size of hypercall parameter

[Ian Campbell]

On Fri, 2014-10-10 at 08:52 +0800, Anh Dinh wrote:
> I wrote a hypercall that takes in a pointer to memory region:
> 
> 
> void do_test(char *p){
> ... // do something with the memory in the hypervisor space
> }
> 
> 
> and invoke it in both Dom0 and DomU through privcmd. 
> 
> 
> But when I pass a memory region of tens of KB (not very large), the
> system crashes and reboots. 

You haven't given us very much to go on, at least the hypervisor code
doing the accesses and the userspace code which invokes it would be
needed for anyone to point out what is wrong.

One hint though: You'll notice that no other hypercall takes a raw
pointer as you have shown above, they all use the XEN_GUEST_HANDLE_PARAM
construct and the associated accessors.

Ian.