Re: [Xen-devel] [PATCH RFC] xen/pvh: use a custom IO bitmap for PVH hardware domains

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/04/15 11:01, Roger Pau Monnà wrote:
> El 08/04/15 a les 14.57, Roger Pau Monne ha escrit:
>> Since a PVH hardware domain has access to the physical hardware create a
>> custom more permissive IO bitmap. The permissions set on the bitmap are
>> populated based on the contents of the ioports rangeset.
>>
>> Also add the IO ports of the serial console used by Xen to the list of not
>> accessible IO ports.
> 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?

In the case of PCI passthrough, the guest may need to use a devices IO BARs.

However, PCI passthrough and PVH is still a very open question, so
making a change here isn't really breaking anything.

> 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.

If anything, ~0 is what should be returned to match real hardware.

~Andrew

>
> Also, once this is set the PVH Specification document should be updated
> to reflect what can guests expect when poking at IO ports.
>
> Roger.


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