Re: [Xen-devel] [v7][PATCH 03/16] xen/passthrough: extend hypercall to support rdm reservation policy

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 07/10/2015 04:01 PM, Jan Beulich wrote:
>>>> On 10.07.15 at 15:26, <George.Dunlap@xxxxxxxxxxxxx> wrote:
>> I also said that if we went with anything other than STRICT that we'd
>> need to check to make sure that the domain really was the hardware
>> domain before proceeding, in case the assumption that pdev->domain ==
>> hardware_domain ever changed.  (Perhaps with an ASSERT -- Jan, what do
>> you think?)
> 
> Yes, such an ASSERT() seems okay/desirable.
> 
>> Also, passing in RELAXED in locations where the flag is completely
>> ignored (such as when removing mappings) doesn't really make any
>> sense.
>>
>> On the whole I think it would be better if you removed the RELAXED
>> flag for both removals and for hardware domains.
> 
> But what would he pass instead? Or wait - iirc I had even suggested
> a way to do so by combining two arguments. Would need to go dig
> that out, because I think the idea got dropped without good reason.

No, I just meant to pass '0' for the flags (which would imply STRICT).

I was saying two things in the above paragraph:

1. For removal, there's no point in passing in anything other than '0'
for flags, since it's ignored.  Passing a non-0 value implies that the
flags will have some effect, which is misleading.

2. For places we know we're adding to hw domains, I think it makes most
sense also to pass in '0', to imply STRICT.

But if instead they insist on passing RELAXED, then please add an
ASSERT(pdev->domain == hw_domain) or something of the kind to
intel_iommu_add_device().  (If defaulting to STRICT, I don't think the
ASSERT is necessary anymore.)

 -George


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