Re: [Qemu-devel] [PATCH RFC v3 12/14] intel_iommu: do replay when context invalidate

[Jason Wang <jasowang@redhat.com>]

On 2017年01月16日 16:18, Peter Xu wrote:
> On Mon, Jan 16, 2017 at 03:52:10PM +0800, Jason Wang wrote:
>>
>> On 2017年01月16日 15:43, Peter Xu wrote:
>>> On Mon, Jan 16, 2017 at 01:53:54PM +0800, Jason Wang wrote:
>>>> On 2017年01月13日 11:06, Peter Xu wrote:
>>>>> Before this one we only invalidate context cache when we receive context
>>>>> entry invalidations. However it's possible that the invalidation also
>>>>> contains a domain switch (only if cache-mode is enabled for vIOMMU).
>>>> So let's check for CM before replaying?
>>> When CM is not set, there should have no device needs
>>> IOMMU_NOTIFIER_MAP notifies. So IMHO it won't hurt if we replay here
>>> (so the notifier_list will only contain UNMAP notifiers at most, and
>>> sending UNMAP to those devices should not affect them at all).
>>>
>>> If we check CM before replay, it'll be faster when guest change iommu
>>> domain for a specific device. But after all this kind of operation is
>>> extremely rare, while if we check CM bit, we have a "assumption" in
>>> the code that MAP is depending on CM. In that case, to make the codes
>>> cleaner, I'd slightly prefer not check it here. How do you think?
>> Ok, I think maybe it's better to add a comment here.
> How about this?
>
> +                /*
> +                 * So a device is moving out of (or moving into) a
> +                 * domain, a replay() suites here to notify all the
> +                 * IOMMU_NOTIFIER_MAP registers about this change.
> +                 * This won't bring bad even if we have no such
> +                 * notifier registered - the IOMMU notification
> +                 * framework will skip MAP notifications if that
> +                 * happened.
> +                 */
>                   memory_region_iommu_replay_all(&vtd_as->iommu);
>
> Thanks,
>
> -- peterx

I'm fine with this.

Thanks