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Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag |
Date: |
Wed, 7 Sep 2016 16:41:54 +1000 |
User-agent: |
Mutt/1.7.0 (2016-08-17) |
On Wed, Sep 07, 2016 at 02:34:19PM +0800, Peter Xu wrote:
> On Wed, Sep 07, 2016 at 03:44:19PM +1000, David Gibson wrote:
> > > For "CHANGE", it sounds like a unmap() + a map(). However I'd say
> > > "ADDITION" is nowhere better...
> >
> > Right.. this brings up a good point.
> >
> > Changing a mapping (i.e. overwriting an existing mapping with a
> > different one) would also need notification, even on x86, no? Since
> > it implicitly invalidates the previous mapping.
> >
> > I'm guessing the guest will avoid this by always unmapping before it
> > maps. We still need to consider this possibility when designing the
> > notifier interface though.
> >
> > It seems the real notification triggers here are:
> > * map - something is mapped which previously wasn't
> > * unmap - something is no longer mapped which was before
> >
> > Note that whether the second needs to be triggered depends on the
> > *previous* state of that IOBA range, *not* on the permissions of the
> > new mapping (if any).
> >
> > A "change" - replacing one mapping with another should count as both a
> > "map" and "unmap" event.
>
> Yeah... For MAP/UNMAP, it is strange in another way: e.g. for vhost,
> it doesn't care about map/unmap, it cares about invalidated cache.
I think caring about invalidated cache *is* caring about unmap. It
doesn't matter whether the new mapping is something or nothing - if
the old mapping is no longer valid, you need to invalidate the cache,
yes?
> So
> IIUC this is a question about "naming" but not the implementations...
> I suppose it is really a matter of taste, and both work for me (either
> INVALIDATION/CHANGE or UNMAP/MAP).
No.. it is a question of implementation. My point is that I don't
think the new permission is sufficient information to let you know if
a notification is necessary. You need to know if there was an
existing mapping at that IOBA.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, (continued)
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Paolo Bonzini, 2016/09/05
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/05
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Paolo Bonzini, 2016/09/05
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/06
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Paolo Bonzini, 2016/09/06
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/06
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Paolo Bonzini, 2016/09/06
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/06
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, David Gibson, 2016/09/07
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/07
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag,
David Gibson <=
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/08
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, David Gibson, 2016/09/11
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/12
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, David Gibson, 2016/09/14
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/14
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, David Gibson, 2016/09/06
- Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, Peter Xu, 2016/09/06
Re: [Qemu-devel] [PATCH 2/3] memory: add iommu_notify_flag, David Gibson, 2016/09/06
[Qemu-devel] [PATCH 3/3] intel_iommu: allow IOMMU_NONE typed notifiers, Peter Xu, 2016/09/05