Re: [Qemu-devel] [PATCH v6 0/3] IOMMU: intel_iommu support map and unmap notifications

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Nov 10, 2016 at 12:44:47PM -0700, Alex Williamson wrote:
> On Thu, 10 Nov 2016 21:20:36 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Thu, Nov 10, 2016 at 09:04:13AM -0700, Alex Williamson wrote:
> > > On Thu, 10 Nov 2016 17:54:35 +0200
> > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > >   
> > > > On Thu, Nov 10, 2016 at 08:30:21AM -0700, Alex Williamson wrote:  
> > > > > On Thu, 10 Nov 2016 17:14:24 +0200
> > > > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > > > >     
> > > > > > On Tue, Nov 08, 2016 at 01:04:21PM +0200, Aviv B.D wrote:    
> > > > > > > From: "Aviv Ben-David" <bd.aviv@gmail.com>
> > > > > > > 
> > > > > > > * 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.      
> > > > > > 
> > > > > > This looks sane I think. Alex, care to comment?
> > > > > > Merging will have to wait until after the release.
> > > > > > Pls remember to re-test and re-ping then.    
> > > > > 
> > > > > I don't think it's suitable for upstream until there's a reasonable
> > > > > replay mechanism    
> > > > 
> > > > Could you pls clarify what do you mean by replay?
> > > > Is this when you attach a device by hotplug to
> > > > a running system?
> > > > 
> > > > If yes this can maybe be addressed by disabling hotplug temporarily.  
> > > 
> > > No, hotplug is not required, moving a device between existing domains
> > > requires replay, ie. actually using it for nested device assignment.  
> > 
> > Good point, that one is a correctness thing. Aviv,
> > could you add this in TODO list in a cover letter pls?
> > 
> > > > > and we straighten out whether it's expected to get
> > > > > multiple notifies and the notif-ee is responsible for filtering
> > > > > them or if the notif-er should do filtering.    
> > > > 
> > > > OK this is a documentation thing.  
> > > 
> > > Well no, it needs to be decided and if necessary implemented.  
> > 
> > Let's assume it's the notif-ee for now. Less is more and all that.
> 
> I think this is opposite of the approach dwg suggested.
>  
> > > > >  Without those, this is
> > > > > effectively just an RFC.    
> > > > 
> > > > It's infrastructure without users so it doesn't break things,
> > > > I'm more interested in seeing whether it's broken in
> > > > some way than whether it's complete.  
> > > 
> > > If it allows use with vfio but doesn't fully implement the complete set
> > > of interfaces, it does break things.  We currently prevent viommu usage
> > > with vfio because it is incomplete.  
> > 
> > Right - that bit is still in as far as I can see.
> 
> Nope, 3/3 changes vtd_iommu_notify_flag_changed() to allow use with
> vfio even though it's still incomplete.  We would at least need
> something like a replay callback for VT-d that triggers an abort if you
> still want to accept it incomplete.  Thanks,
> 
> Alex

IIUC practically things seems to work, right?
So how about disabling by default with a flag for people that want to
experiment with it?
E.g. x-vfio-allow-broken-translations ?

I would like to help this make progress such that 1. Aviv
gets the credit he did so far and 2. more people can join
development and help complete it.

> > > > The patchset spent out of tree too long and I'd like to see
> > > > us make progress towards device assignment working with
> > > > vIOMMU sooner rather than later, so if it's broken I won't
> > > > merge it but if it's incomplete I will.  
> > > 
> > > So long as it's incomplete and still prevents vfio usage, I'm ok with
> > > merging it, but I don't want to enable vfio usage until it's complete.
> > > Thanks,
> > > 
> > > Alex
> > >   
> > > > > > > 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.
> > > > > > > * 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.
> > > > > > > * vfio_iommu_map_notify should check if address space range is suitable for 
> > > > > > >   current notifier.
> > > > > > > 
> > > > > > > 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.
> > > > > > > 
> > > > > > > Changes from v4 to v5:
> > > > > > > * Reduce the number of changes in patch 2 and make flags real bitfield.
> > > > > > > * Revert deleted debug prints.
> > > > > > > * Fix memory leak in patch 3.
> > > > > > > 
> > > > > > > Changes from v5 to v6:
> > > > > > > * fix prototype of iommu_translate function for more IOMMU types.
> > > > > > > * VFIO will be notified only on the difference, without unmap 
> > > > > > >   before change to maps.
> > > > > > > 
> > > > > > > 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/alpha/typhoon.c             |   2 +-
> > > > > > >  hw/i386/amd_iommu.c            |   4 +-
> > > > > > >  hw/i386/intel_iommu.c          | 160 +++++++++++++++++++++++++++++++++--------
> > > > > > >  hw/i386/intel_iommu_internal.h |   3 +
> > > > > > >  hw/pci-host/apb.c              |   2 +-
> > > > > > >  hw/ppc/spapr_iommu.c           |   2 +-
> > > > > > >  hw/s390x/s390-pci-bus.c        |   2 +-
> > > > > > >  include/exec/memory.h          |   6 +-
> > > > > > >  include/hw/i386/intel_iommu.h  |  11 +++
> > > > > > >  memory.c                       |   3 +-
> > > > > > >  11 files changed, 160 insertions(+), 38 deletions(-)
> > > > > > > 
> > > > > > > -- 
> > > > > > > 1.9.1      
> > > > > >