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Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map an
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications |
Date: |
Tue, 18 Oct 2016 16:52:04 +1100 |
User-agent: |
Mutt/1.7.0 (2016-08-17) |
On Mon, Oct 17, 2016 at 10:47:02PM -0600, Alex Williamson wrote:
> On Tue, 18 Oct 2016 15:06:55 +1100
> David Gibson <address@hidden> wrote:
>
> > On Mon, Oct 17, 2016 at 10:07:36AM -0600, Alex Williamson wrote:
> > > On Mon, 17 Oct 2016 18:44:21 +0300
> > > "Aviv B.D" <address@hidden> wrote:
> > >
> > > > From: "Aviv Ben-David" <address@hidden>
> > > >
> > > > * Advertize Cache Mode capability in iommu cap register.
> > > > This capability is controlled by "cache-mode" property of intel-iommu
> > > > device.
> > > > To enable this option call QEMU with "-device
> > > > intel-iommu,cache-mode=true".
> > > >
> > > > * On page cache invalidation in intel vIOMMU, check if the domain
> > > > belong to
> > > > registered notifier, and notify accordingly.
> > > >
> > > > Currently this patch still doesn't enabling VFIO devices support with
> > > > vIOMMU
> > > > present. Current problems:
> > > > * vfio_iommu_map_notify is not aware about memory range belong to
> > > > specific
> > > > VFIOGuestIOMMU.
> > >
> > > Could you elaborate on why this is an issue?
> > >
> > > > * memory_region_iommu_replay hangs QEMU on start up while it itterate
> > > > over
> > > > 64bit address space. Commenting out the call to this function enables
> > > > workable VFIO device while vIOMMU present.
> > >
> > > This has been discussed previously, it would be incorrect for vfio not
> > > to call the replay function. The solution is to add an iommu driver
> > > callback to efficiently walk the mappings within a MemoryRegion.
> >
> > Right, replay is a bit of a hack. There are a couple of other
> > approaches that might be adequate without a new callback:
> > - Make the VFIOGuestIOMMU aware of the guest address range mapped
> > by the vIOMMU. Intel currently advertises that as a full 64-bit
> > address space, but I bet that's not actually true in practice.
> > - Have the IOMMU MR advertise a (minimum) page size for vIOMMU
> > mappings. That may let you stpe through the range with greater
> > strides
>
> Hmm, VT-d supports at least a 39-bit address width and always supports
> a minimum 4k page size, so yes that does reduce us from 2^52 steps down
> to 2^27,
Right, which is probably doable, if not ideal
> but it's still absurd to walk through the raw address space.
Well.. it depends on the internal structure of the IOMMU. For Power,
it's traditionally just a 1-level page table, so we can't actually do
any better than stepping through each IOMMU page.
> It does however seem correct to create the MemoryRegion with a width
> that actually matches the IOMMU capability, but I don't think that's a
> sufficient fix by itself. Thanks,
I suspect it would actually make it workable in the short term.
But I don't disagree that a "traverse" or "replay" callback of some
sort in the iommu_ops is a better idea long term. Having a fallback
to the current replay implementation if the callback isn't supplied
seems pretty reasonable though.
--
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 v4 RESEND 3/3] IOMMU: enable intel_iommu map and unmap notifiers, (continued)
Re: [Qemu-devel] [PATCH v4 RESEND 3/3] IOMMU: enable intel_iommu map and unmap notifiers, Peter Xu, 2016/10/20
[Qemu-devel] [PATCH v4 RESEND 2/3] IOMMU: change iommu_op->translate's is_write to flags, add support to NO_FAIL flag mode, Aviv B.D, 2016/10/17
Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications, Alex Williamson, 2016/10/17
Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications, Aviv B.D., 2016/10/20
- Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications, Alex Williamson, 2016/10/20
- Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications, David Gibson, 2016/10/20
- Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications, Peter Xu, 2016/10/21
- Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications, Alex Williamson, 2016/10/21
- Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications, Peter Xu, 2016/10/31
Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications, David Gibson, 2016/10/24