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memory: emulate ioeventfd

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The ioeventfd mechanism is used by vhost, dataplane, and virtio-pci to
turn guest MMIO/PIO writes into eventfd file descriptor events.  This
allows arbitrary threads to be notified when the guest writes to a
specific MMIO/PIO address.

qtest and TCG do not support ioeventfd because memory writes are not
checked against registered ioeventfds in QEMU.  This patch implements
this in memory_region_dispatch_write() so qtest can use ioeventfd.

Also this patch fixes vhost aborting on some misconfigured old kernels
like 3.18.0 on ARM. It is possible to explicitly enable CONFIG_EVENTFD
in expert settings, while MMIO binding support in KVM will still be
missing.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
Message-Id: <006e01d12377$0b9c2d40$22d487c0$@samsung.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Pavel Fedin 2015-11-20 12:37:16 +03:00 • committed by Paolo Bonzini
parent bc92e4e97e
commit 8c56c1a592
2 changed files with 46 additions and 2 deletions
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6
kvm-all.c
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@ -1628,8 +1628,10 @@ static int kvm_init(MachineState *ms)
kvm_state = s;
s->memory_listener.listener.eventfd_add = kvm_mem_ioeventfd_add;
s->memory_listener.listener.eventfd_del = kvm_mem_ioeventfd_del;
if (kvm_eventfds_allowed) {
s->memory_listener.listener.eventfd_add = kvm_mem_ioeventfd_add;
s->memory_listener.listener.eventfd_del = kvm_mem_ioeventfd_del;
}
s->memory_listener.listener.coalesced_mmio_add = kvm_coalesce_mmio_region;
s->memory_listener.listener.coalesced_mmio_del = kvm_uncoalesce_mmio_region;