On 20/08/14 11:19, Wei Hu wrote:
> Hello,
> Sending to Xen, drivers and virtualization mailing lists since this might be 
> of interest to the folks on these aliases.
> I am working for Microsoft to improve the performance of FreeBSD running on 
> Hyper-V. Right now I am adding a feature in the vmbus driver which could 
> handle the host-guest channel communications on all vCPUs simultaneously. In 
> order to achieve this, the hypervisor will send same interrupt concurrently 
> on all the vCPUs. The traditional way on FreeBSD to set up interrupt handling 
> for devicse, such as calling bus_alloc_resource() to reserve an IRQ line, and 
> then calling bus_setup_intr() to create a vector, doesn't seem to work in 
> this case. It seems if the interrupt is routed via legacy IRQ, it can only be 
> active on one vCPU at a time. In order to allow the same interrupt to be 
> handled on all vCPUs concurrently, all I need is an IDT entry, not an IRQ 
> line.
> I checked current FreeBSD code. It looks to me Xen directly uses the vector 
> number IDT_EVTCHN (0x93) to achieve the same purpose. I am proposing both Xen 
> and Hyper-V share this same vector. Following is a little bit detail of my 
> proposal for the changes in the current kernel.
> 1.       In machdep.c:
>  #ifdef XENHVM
>         setidt(IDT_EVTCHN, &IDTVEC(xen_intr_upcall), SDT_SYSIGT, SEL_UPL, 0);
> #else
>         setidt(IDT_EVTCHN, &IDTVEC(hv_vmbus_intr), SDT_SYSIGT, SEL_UPL, 0);
> #endif
> 2.       Apic_vector.S
> Add IDTVEC(hv_vmbus_intr) to call Hyper-V vmbus interrupt service routine.
> Any  thoughts, objections and feedbacks are all welcome.


I don't think using the same IDT vector is the right approach, I would
just pick a different IDT vector and use that for Hyper-V. Using the
same IDT vector (like your suggestion above) would prevent shipping a
kernel with with both Hyper-V and Xen support (like it's done now in


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