Patch "vfio: Introduce interface to flush virqfd inject workqueue" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    vfio: Introduce interface to flush virqfd inject workqueue

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     vfio-introduce-interface-to-flush-virqfd-inject-work.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 57805a44ab6bd22ffe34bb46c97b2e80c0e12044
Author: Alex Williamson <alex.williamson@xxxxxxxxxx>
Date:   Fri Mar 8 16:05:24 2024 -0700

    vfio: Introduce interface to flush virqfd inject workqueue
    
    [ Upstream commit b620ecbd17a03cacd06f014a5d3f3a11285ce053 ]
    
    In order to synchronize changes that can affect the thread callback,
    introduce an interface to force a flush of the inject workqueue.  The
    irqfd pointer is only valid under spinlock, but the workqueue cannot
    be flushed under spinlock.  Therefore the flush work for the irqfd is
    queued under spinlock.  The vfio_irqfd_cleanup_wq workqueue is re-used
    for queuing this work such that flushing the workqueue is also ordered
    relative to shutdown.
    
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
    Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240308230557.805580-4-alex.williamson@xxxxxxxxxx
    Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
    Stable-dep-of: 18c198c96a81 ("vfio/pci: Create persistent INTx handler")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/vfio/virqfd.c b/drivers/vfio/virqfd.c
index 29c564b7a6e13..5322691338019 100644
--- a/drivers/vfio/virqfd.c
+++ b/drivers/vfio/virqfd.c
@@ -101,6 +101,13 @@ static void virqfd_inject(struct work_struct *work)
 		virqfd->thread(virqfd->opaque, virqfd->data);
 }
 
+static void virqfd_flush_inject(struct work_struct *work)
+{
+	struct virqfd *virqfd = container_of(work, struct virqfd, flush_inject);
+
+	flush_work(&virqfd->inject);
+}
+
 int vfio_virqfd_enable(void *opaque,
 		       int (*handler)(void *, void *),
 		       void (*thread)(void *, void *),
@@ -124,6 +131,7 @@ int vfio_virqfd_enable(void *opaque,
 
 	INIT_WORK(&virqfd->shutdown, virqfd_shutdown);
 	INIT_WORK(&virqfd->inject, virqfd_inject);
+	INIT_WORK(&virqfd->flush_inject, virqfd_flush_inject);
 
 	irqfd = fdget(fd);
 	if (!irqfd.file) {
@@ -213,3 +221,16 @@ void vfio_virqfd_disable(struct virqfd **pvirqfd)
 	flush_workqueue(vfio_irqfd_cleanup_wq);
 }
 EXPORT_SYMBOL_GPL(vfio_virqfd_disable);
+
+void vfio_virqfd_flush_thread(struct virqfd **pvirqfd)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&virqfd_lock, flags);
+	if (*pvirqfd && (*pvirqfd)->thread)
+		queue_work(vfio_irqfd_cleanup_wq, &(*pvirqfd)->flush_inject);
+	spin_unlock_irqrestore(&virqfd_lock, flags);
+
+	flush_workqueue(vfio_irqfd_cleanup_wq);
+}
+EXPORT_SYMBOL_GPL(vfio_virqfd_flush_thread);
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 89b265bc6ec31..8b1a298204091 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -356,6 +356,7 @@ struct virqfd {
 	wait_queue_entry_t		wait;
 	poll_table		pt;
 	struct work_struct	shutdown;
+	struct work_struct	flush_inject;
 	struct virqfd		**pvirqfd;
 };
 
@@ -363,5 +364,6 @@ int vfio_virqfd_enable(void *opaque, int (*handler)(void *, void *),
 		       void (*thread)(void *, void *), void *data,
 		       struct virqfd **pvirqfd, int fd);
 void vfio_virqfd_disable(struct virqfd **pvirqfd);
+void vfio_virqfd_flush_thread(struct virqfd **pvirqfd);
 
 #endif /* VFIO_H */