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Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM t
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest |
Date: |
Mon, 21 Nov 2016 15:35:44 +0200 |
On Fri, Nov 11, 2016 at 12:15:48PM +0800, Jason Wang wrote:
>
>
> On 2016年11月11日 11:39, Michael S. Tsirkin wrote:
> > On Fri, Nov 11, 2016 at 10:32:42AM +0800, Jason Wang wrote:
> > >
> > > On 2016年11月10日 06:00, Michael S. Tsirkin wrote:
> > > > On Wed, Nov 09, 2016 at 03:28:02PM +0800, Jason Wang wrote:
> > > > > >
> > > > > > On 2016年11月08日 19:04, Aviv B.D wrote:
> > > > > > > > From: "Aviv Ben-David"<address@hidden>
> > > > > > > >
> > > > > > > > This capability asks the guest to invalidate cache before each
> > > > > > > > map operation.
> > > > > > > > We can use this invalidation to trap map operations in the
> > > > > > > > hypervisor.
> > > > > > Hi:
> > > > > >
> > > > > > Like I've asked twice in the past, I want to know why don't you
> > > > > > cache
> > > > > > translation faults as what spec required (especially this is a
> > > > > > guest visible
> > > > > > behavior)?
> > > > > >
> > > > > > Btw, please cc me on posting future versions.
> > > > > >
> > > > > > Thanks
> > > > Caching isn't guest visible.
> > > Seems not, if one fault mapping were cached by IOTLB. Guest can notice
> > > this
> > > behavior.
> > Sorry, I don't get what you are saying.
> >
> > > > Spec just says you*can* cache,
> > > > not that you must.
> > > >
> > > Yes, but what did in this patch is "don't". What I suggest is just a
> > > "can",
> > > since anyway the IOTLB entries were limited and could be replaced by
> > > other.
> > >
> > > Thanks
> > Have trouble understanding this. Can you given an example of
> > a guest visible difference?
>
> I guess this may do the detection:
>
> 1) map iova A to be non-present.
> 2) invalidate iova A
> 3) map iova A to addr B
> 4) access iova A
>
> A correct implemented CM may meet fault in step 4, but with this patch, we
> never.
I think that IOTLB is free to invalidate entries at any point,
so the fault is not guaranteed on bare metal.
--
MST
- [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Aviv B.D, 2016/11/08
- [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Aviv B.D, 2016/11/08
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Jason Wang, 2016/11/09
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Michael S. Tsirkin, 2016/11/09
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Jason Wang, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Michael S. Tsirkin, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Jason Wang, 2016/11/10
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Aviv B.D., 2016/11/21
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Jason Wang, 2016/11/21
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Jason Wang, 2016/11/21
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Aviv B.D., 2016/11/22
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Michael S. Tsirkin, 2016/11/22
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Michael S. Tsirkin, 2016/11/22
- Re: [Qemu-devel] [PATCH v6 1/3] IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to guest, Tian, Kevin, 2016/11/30
[Qemu-devel] [PATCH v6 3/3] IOMMU: enable intel_iommu map and unmap notifiers, Aviv B.D, 2016/11/08
[Qemu-devel] [PATCH v6 2/3] IOMMU: change iommu_op->translate's is_write to flags, add support to NO_FAIL flag mode, Aviv B.D, 2016/11/08
Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications, Michael S. Tsirkin, 2016/11/10