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

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Message-ID: <20151108191056-mutt-send-email-mst@redhat.com>
Date:	Sun, 8 Nov 2015 19:11:28 +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 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?
Did patches ever get posted?

> 
> 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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