>>> On 14.04.15 at 12:01, <roger....@citrix.com> wrote:
> I have one question about the current IO port handling for PVH guests
> (DomU and Dom0). There's some code right now in vmx_vmexit_handler
> (EXIT_REASON_IO_INSTRUCTION) that's kind PVH specific:
>
> if ( exit_qualification & 0x10 )
> {
> /* INS, OUTS */
> if ( unlikely(is_pvh_vcpu(v)) /* PVH fixme */ ||
> !handle_mmio() )
> hvm_inject_hw_exception(TRAP_gp_fault, 0);
> }
> else
> {
> /* IN, OUT */
> uint16_t port = (exit_qualification >> 16) & 0xFFFF;
> int bytes = (exit_qualification & 0x07) + 1;
> int dir = (exit_qualification & 0x08) ? IOREQ_READ : IOREQ_WRITE;
>
> if ( handle_pio(port, bytes, dir) )
> update_guest_eip(); /* Safe: IN, OUT */
> }
>
> Is there any need for DomUs to access the IO ports? I know that FreeBSD
> will poke at some of them during boot to scan for devices, but I'm not
> sure if we could just make them noops in the PVH case and simply return
> garbage.
The PVH special case quoted above is there only to prevent
reaching handle_mmio(). The non-string "else" path was enabled
solely on the basis that it was possible to be made work without
much extra effort. And while (without pass-through) it shouldn't
be needed for PVH DomU-s, it also should do no harm.
Jan
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
