Re: [PATCH V6 0/6] Fast mmio eventfd fixes

[Jason Wang <jasowang@redhat.com>]

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

>
>> 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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