Date:	Fri, 6 Sep 2013 09:01:47 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Alexander Graf <agraf@...e.de>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v9 12/13] KVM: PPC: Add support for IOMMU in-kernel
 handling

On Fri, Sep 06, 2013 at 09:38:21AM +1000, Alexey Kardashevskiy wrote:
> On 09/06/2013 04:10 AM, Gleb Natapov wrote:
> > On Wed, Sep 04, 2013 at 02:01:28AM +1000, Alexey Kardashevskiy wrote:
> >> On 09/03/2013 08:53 PM, Gleb Natapov wrote:
> >>> On Mon, Sep 02, 2013 at 01:14:29PM +1000, Alexey Kardashevskiy wrote:
> >>>> On 09/01/2013 10:06 PM, Gleb Natapov wrote:
> >>>>> On Wed, Aug 28, 2013 at 06:50:41PM +1000, Alexey Kardashevskiy wrote:
> >>>>>> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
> >>>>>> and H_STUFF_TCE requests targeted an IOMMU TCE table without passing
> >>>>>> them to user space which saves time on switching to user space and back.
> >>>>>>
> >>>>>> Both real and virtual modes are supported. The kernel tries to
> >>>>>> handle a TCE request in the real mode, if fails it passes the request
> >>>>>> to the virtual mode to complete the operation. If it a virtual mode
> >>>>>> handler fails, the request is passed to user space.
> >>>>>>
> >>>>>> The first user of this is VFIO on POWER. Trampolines to the VFIO external
> >>>>>> user API functions are required for this patch.
> >>>>>>
> >>>>>> This adds a "SPAPR TCE IOMMU" KVM device to associate a logical bus
> >>>>>> number (LIOBN) with an VFIO IOMMU group fd and enable in-kernel handling
> >>>>>> of map/unmap requests. The device supports a single attribute which is
> >>>>>> a struct with LIOBN and IOMMU fd. When the attribute is set, the device
> >>>>>> establishes the connection between KVM and VFIO.
> >>>>>>
> >>>>>> Tests show that this patch increases transmission speed from 220MB/s
> >>>>>> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
> >>>>>>
> >>>>>> Signed-off-by: Paul Mackerras <paulus@...ba.org>
> >>>>>> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
> >>>>>>
> >>>>>> ---
> >>>>>>
> >>>>>> Changes:
> >>>>>> v9:
> >>>>>> * KVM_CAP_SPAPR_TCE_IOMMU ioctl to KVM replaced with "SPAPR TCE IOMMU"
> >>>>>> KVM device
> >>>>>> * release_spapr_tce_table() is not shared between different TCE types
> >>>>>> * reduced the patch size by moving VFIO external API
> >>>>>> trampolines to separate patche
> >>>>>> * moved documentation from Documentation/virtual/kvm/api.txt to
> >>>>>> Documentation/virtual/kvm/devices/spapr_tce_iommu.txt
> >>>>>>
> >>>>>> v8:
> >>>>>> * fixed warnings from check_patch.pl
> >>>>>>
> >>>>>> 2013/07/11:
> >>>>>> * removed multiple #ifdef IOMMU_API as IOMMU_API is always enabled
> >>>>>> for KVM_BOOK3S_64
> >>>>>> * kvmppc_gpa_to_hva_and_get also returns host phys address. Not much sense
> >>>>>> for this here but the next patch for hugepages support will use it more.
> >>>>>>
> >>>>>> 2013/07/06:
> >>>>>> * added realmode arch_spin_lock to protect TCE table from races
> >>>>>> in real and virtual modes
> >>>>>> * POWERPC IOMMU API is changed to support real mode
> >>>>>> * iommu_take_ownership and iommu_release_ownership are protected by
> >>>>>> iommu_table's locks
> >>>>>> * VFIO external user API use rewritten
> >>>>>> * multiple small fixes
> >>>>>>
> >>>>>> 2013/06/27:
> >>>>>> * tce_list page is referenced now in order to protect it from accident
> >>>>>> invalidation during H_PUT_TCE_INDIRECT execution
> >>>>>> * added use of the external user VFIO API
> >>>>>>
> >>>>>> 2013/06/05:
> >>>>>> * changed capability number
> >>>>>> * changed ioctl number
> >>>>>> * update the doc article number
> >>>>>>
> >>>>>> 2013/05/20:
> >>>>>> * removed get_user() from real mode handlers
> >>>>>> * kvm_vcpu_arch::tce_tmp usage extended. Now real mode handler puts there
> >>>>>> translated TCEs, tries realmode_get_page() on those and if it fails, it
> >>>>>> passes control over the virtual mode handler which tries to finish
> >>>>>> the request handling
> >>>>>> * kvmppc_lookup_pte() now does realmode_get_page() protected by BUSY bit
> >>>>>> on a page
> >>>>>> * The only reason to pass the request to user mode now is when the user mode
> >>>>>> did not register TCE table in the kernel, in all other cases the virtual mode
> >>>>>> handler is expected to do the job
> >>>>>> ---
> >>>>>>  .../virtual/kvm/devices/spapr_tce_iommu.txt        |  37 +++
> >>>>>>  arch/powerpc/include/asm/kvm_host.h                |   4 +
> >>>>>>  arch/powerpc/kvm/book3s_64_vio.c                   | 310 ++++++++++++++++++++-
> >>>>>>  arch/powerpc/kvm/book3s_64_vio_hv.c                | 122 ++++++++
> >>>>>>  arch/powerpc/kvm/powerpc.c                         |   1 +
> >>>>>>  include/linux/kvm_host.h                           |   1 +
> >>>>>>  virt/kvm/kvm_main.c                                |   5 +
> >>>>>>  7 files changed, 477 insertions(+), 3 deletions(-)
> >>>>>>  create mode 100644 Documentation/virtual/kvm/devices/spapr_tce_iommu.txt
> >>>>>>
> >>>>>> diff --git a/Documentation/virtual/kvm/devices/spapr_tce_iommu.txt b/Documentation/virtual/kvm/devices/spapr_tce_iommu.txt
> >>>>>> new file mode 100644
> >>>>>> index 0000000..4bc8fc3
> >>>>>> --- /dev/null
> >>>>>> +++ b/Documentation/virtual/kvm/devices/spapr_tce_iommu.txt
> >>>>>> @@ -0,0 +1,37 @@
> >>>>>> +SPAPR TCE IOMMU device
> >>>>>> +
> >>>>>> +Capability: KVM_CAP_SPAPR_TCE_IOMMU
> >>>>>> +Architectures: powerpc
> >>>>>> +
> >>>>>> +Device type supported: KVM_DEV_TYPE_SPAPR_TCE_IOMMU
> >>>>>> +
> >>>>>> +Groups:
> >>>>>> +  KVM_DEV_SPAPR_TCE_IOMMU_ATTR_LINKAGE
> >>>>>> +  Attributes: single attribute with pair { LIOBN, IOMMU fd}
> >>>>>> +
> >>>>>> +This is completely made up device which provides API to link
> >>>>>> +logical bus number (LIOBN) and IOMMU group. The user space has
> >>>>>> +to create a new SPAPR TCE IOMMU device per a logical bus.
> >>>>>> +
> >>>>> Why not have one device that can handle multimple links?
> >>>>
> >>>>
> >>>> I can do that. If I make it so, it won't even look as a device at all, just
> >>>> some weird interface to KVM but ok. What bothers me is it is just a
> >>> May be I do not understand usage pattern here. Why do you feel that device
> >>> that can handle multiple links is worse than device per link? How many logical
> >>> buses is there usually? How often they created/destroyed? I am not insisting
> >>> on the change, just trying to understand why you do not like it.
> >>
> >>
> >> Is it usually one PCI host bus adapter per IOMMU group which is usually
> >> one PCI card or 2-3 cards if it is a legacy PCI-X, and they are created
> >> when QEMU-KVM starts. Not many. And they live till KVM ends.
> >>
> >> My point is why would I want to put all links to one device? It all is just
> >> a matter of taste and nothing more. Or I am missing something but I do not
> >> see what. If it is all about making thing to be kosher/halal/orthodox, then
> >> I have more stuff to do, like reworking the emulated TCEs. But if is it for
> >> (I do not know, just guessing) performance or something like that - then
> >> I'll fix it, I just need to know what I am fixing.
> >>
> > Each device creates an fd, if you can have a lot of them eventually this
> > will be a bottleneck. You are saying this is not the case, so lets go
> > with proposed interface.
> 
> 
> Did you decide not to answer the email which Ben sent yesterday or you just
> did not see it? Just checking :)
> 
Haven't seen it. Which one?

--
			Gleb.
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