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

[Peter Xu]

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