Re: [Qemu-devel] [PATCH v4 RESEND 0/3] IOMMU: intel_iommu support map and unmap notifications

[David Gibson]

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

> Thanks,
> 
> Alex
> 
> > Changes from v1 to v2:
> > * remove assumption that the cache do not clears
> > * fix lockup on high load.
> > 
> > Changes from v2 to v3:
> > * remove debug leftovers
> > * split to sepearate commits
> > * change is_write to flags in vtd_do_iommu_translate, add IOMMU_NO_FAIL 
> >   to suppress error propagating to guest.
> > 
> > Changes from v3 to v4:
> > * Add property to intel_iommu device to control the CM capability, 
> >   default to False.
> > * Use s->iommu_ops.notify_flag_changed to register notifiers.
> > 
> > Changes from v4 to v4 RESEND:
> > * Fix codding style pointed by checkpatch.pl script.
> > 
> > Aviv Ben-David (3):
> >   IOMMU: add option to enable VTD_CAP_CM to vIOMMU capility exposoed to
> >     guest
> >   IOMMU: change iommu_op->translate's is_write to flags, add support to
> >     NO_FAIL flag mode
> >   IOMMU: enable intel_iommu map and unmap notifiers
> > 
> >  exec.c                         |   3 +-
> >  hw/i386/amd_iommu.c            |   4 +-
> >  hw/i386/intel_iommu.c          | 175 
> > +++++++++++++++++++++++++++++++++--------
> >  hw/i386/intel_iommu_internal.h |   3 +
> >  include/exec/memory.h          |   6 +-
> >  include/hw/i386/intel_iommu.h  |  11 +++
> >  memory.c                       |   3 +-
> >  7 files changed, 168 insertions(+), 37 deletions(-)
> > 
> 
> 

-- 
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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