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

[Jason Wang]

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