Re: [Xen-devel] [Patch] continue_hypercall_on_cpu rework using tasklets

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 14/04/2010 08:25, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx> wrote:

>> A tasklet also takes an arbitrary ulong parameter, which you can cast to a
>> pointer to your informational structure. The parameter is specified via
>> tasklet_init(). That should suffice.
> 
> I'm already using this. The problem is to find the original calling vcpu in
> case of a nested call of continue_hypercall_on_cpu() while not conflicting
> with concurrent calls from other vcpus which happen to address the same pcpu.

There can be only one nested invocation on any given pcpu, since a running
invocation is never preempted. Hence on entry to c_h_o_c() you can check a
per-cpu variable to see whether this invocation is nesting, or not. And if
it is, that variable can be a pointer to an info structure which includes a
pointer to the invoking vcpu.

 -- Keir



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