Date:	Mon, 9 Nov 2015 22:19:19 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	gleb@...nel.org, pbonzini@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, cornelia.huck@...ibm.com
Subject: Re: [PATCH V6 0/6] Fast mmio eventfd fixes

On Mon, Nov 09, 2015 at 12:35:45PM +0800, Jason Wang wrote:
> 
> 
> On 11/09/2015 01:11 AM, Michael S. Tsirkin wrote:
> > On Tue, Sep 15, 2015 at 02:41:53PM +0800, Jason Wang wrote:
> >> Hi:
> >>
> >> This series fixes two issues of fast mmio eventfd:
> >>
> >> 1) A single iodev instance were registerd on two buses: KVM_MMIO_BUS
> >>    and KVM_FAST_MMIO_BUS. This will cause double in
> >>    ioeventfd_destructor()
> >> 2) A zero length iodev on KVM_MMIO_BUS will never be found but
> >>    kvm_io_bus_cmp(). This will lead e.g the eventfd will be trapped by
> >>    qemu instead of host.
> >>
> >> 1 is fixed by allocating two instances of iodev and introduce a new
> >> capability for userspace. 2 is fixed by ignore the actual length if
> >> the length of iodev is zero in kvm_io_bus_cmp().
> >>
> >> Please review.
> >> Changes from V5:
> >> - move patch of explicitly checking for KVM_MMIO_BUS to patch 1 and
> >>   remove the unnecessary checks
> >> - even more grammar and typo fixes
> >> - rabase to kvm.git
> >> - document KVM_CAP_FAST_MMIO
> > What's up with userspace using this capability?
> 
> It was renamed to KVM_CAP_IOEVENTFD_ANY_LENGTH.
> 
> > Did patches ever get posted?
> 
> See https://lkml.org/lkml/2015/9/28/208

Talking about userspace here.
QEMU freeze is approaching, it really should
use this to avoid regressions.


> >
> >> Changes from V4:
> >> - move the location of kvm_assign_ioeventfd() in patch 1 which reduce
> >>   the change set.
> >> - commit log typo fixes
> >> - switch to use kvm_deassign_ioeventfd_id) when fail to register to
> >>   fast mmio bus
> >> - change kvm_io_bus_cmp() as Paolo's suggestions
> >> - introduce a new capability to avoid new userspace crash old kernel
> >> - add a new patch that only try to register mmio eventfd on fast mmio
> >>   bus
> >>
> >> Changes from V3:
> >>
> >> - Don't do search on two buses when trying to do write on
> >>   KVM_MMIO_BUS. This fixes a small regression found by vmexit.flat.
> >> - Since we don't do search on two buses, change kvm_io_bus_cmp() to
> >>   let it can find zero length iodevs.
> >> - Fix the unnecessary lines in tracepoint patch.
> >>
> >> Changes from V2:
> >> - Tweak styles and comment suggested by Cornelia.
> >>
> >> Changes from v1:
> >> - change ioeventfd_bus_from_flags() to return KVM_FAST_MMIO_BUS when
> >>   needed to save lots of unnecessary changes.
> >>
> >> Jason Wang (6):
> >>   kvm: don't try to register to KVM_FAST_MMIO_BUS for non mmio eventfd
> >>   kvm: factor out core eventfd assign/deassign logic
> >>   kvm: fix double free for fast mmio eventfd
> >>   kvm: fix zero length mmio searching
> >>   kvm: add tracepoint for fast mmio
> >>   kvm: add fast mmio capabilitiy
> >>
> >>  Documentation/virtual/kvm/api.txt |   7 ++-
> >>  arch/x86/kvm/trace.h              |  18 ++++++
> >>  arch/x86/kvm/vmx.c                |   1 +
> >>  arch/x86/kvm/x86.c                |   1 +
> >>  include/uapi/linux/kvm.h          |   1 +
> >>  virt/kvm/eventfd.c                | 124 ++++++++++++++++++++++----------------
> >>  virt/kvm/kvm_main.c               |  20 +++++-
> >>  7 files changed, 118 insertions(+), 54 deletions(-)
> >>
> >> -- 
> >> 2.1.4
> > --
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