Re: [Xen-devel] [PATCH v2 2/2] x86/io: move the list of guest to machine IO ports out of domain_iommu

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 04/04/17 12:31, Jan Beulich wrote:
>>>> On 04.04.17 at 13:06, <roger.pau@xxxxxxxxxx> wrote:
>> On Wed, Mar 29, 2017 at 11:49:53AM +0100, Roger Pau Monne wrote:
>>> On Wed, Mar 29, 2017 at 11:41:40AM +0100, Andrew Cooper wrote:
>>>> On 28/03/17 14:12, Roger Pau Monne wrote:
>>>>> There's no reason to store that list inside of the domain_iommu struct, 
>>>>> the
>>>>> forwarding of guest IO ports into machine IO ports is not tied to the 
>>>>> presence
>>>>> of an IOMMU.
>>>>>
>>>>> Move it inside of the hvm_domain struct instead.
>>>>>
>>>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>>> Actually, on second thoughts, I rescind my R-by.
>>>>
>>>> This breaks PV guests, which must not use state in the hvm half of the
>>>> union.
>>> I'm extremely confused now, AFAICT the g2m_ioport_list list is only used by 
>>> the
>>> g2m_portio_* handlers, and those handlers already make use of HVM only 
>>> fields
>>> (ie: hvm_vcpu_io).
>> Can this be committed?
> As said on irc, I think was posted after the last posting date, so you'd
> need to obtain an ack from Julien.
>
>> I understand there's a previous regression here, but
>> this patches don't make it any worse AFAICT, and they clarify the 
>> nomenclature.
> I don't see the "previous regression": The handlers can be invoked
> only for HVM guests. What is not HVM-specific is the domctl, and
> there is where you introduce a regression.

It is certainly the case that in the past, you could use this domctl to
pass ISA ports through to PV guests, and that definitely regressed as
some point in the past.  ISTR Ian (cc'd) fielded a question to this
effect from Debian.

This change definitely puts an HVM-only restriction in place, which is
wrong IMO.

~Andrew

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