virt: acrn: Remove unsued acrn_irqfds_mutex.

acrn_irqfds_mutex is not used, never was.

Remove acrn_irqfds_mutex.

Fixes: aa3b483ff1d71 ("virt: acrn: Introduce irqfd")
Cc: Fei Li <fei1.li@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/YidLo57Kw/u/cpA5@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

virt: acrn: Use EPOLLIN instead of POLLIN

This fixes the following sparse warning:
"sparse warnings: (new ones prefixed by >>)"
>> drivers/virt/acrn/irqfd.c:163:13: sparse: sparse: restricted __poll_t
degrades to integer

Fixes: dcf9625f2adf ("virt: acrn: Use vfs_poll() instead of f_op->poll()")
Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Shuo Liu <shuo.a.liu@intel.com>
Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
Link: https://lore.kernel.org/r/20210310074901.7486-1-yejune.deng@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

virt: acrn: Use vfs_poll() instead of f_op->poll()

Use a more advanced function vfs_poll() in acrn_irqfd_assign().
At the same time, modify the definition of events.

Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
Link: https://lore.kernel.org/r/20210221133306.33530-1-shuo.a.liu@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

virt: acrn: Introduce irqfd

irqfd is a mechanism to inject a specific interrupt to a User VM using a
decoupled eventfd mechanism.

Vhost is a kernel-level virtio server which uses eventfd for interrupt
injection. To support vhost on ACRN, irqfd is introduced in HSM.

HSM provides ioctls to associate a virtual Message Signaled Interrupt
(MSI) with an eventfd. The corresponding virtual MSI will be injected
into a User VM once the eventfd got signal.

Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Yu Wang <yu1.wang@intel.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
Link: https://lore.kernel.org/r/20210207031040.49576-17-shuo.a.liu@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>