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authorDmitry Torokhov <dmitry.torokhov@gmail.com>2023-07-15 01:45:33 +0300
committerAlex Williamson <alex.williamson@redhat.com>2023-08-03 21:01:56 +0300
commit73e2f19da50857a3488f44a7c9d874fed6fae533 (patch)
tree1fada3117e1a97eabf0eef97d35ab43b962fae8a /virt/kvm
parent9e0f4f2918c2ff145d3dedee862d9919a6ed5812 (diff)
downloadlinux-73e2f19da50857a3488f44a7c9d874fed6fae533.tar.xz
kvm/vfio: avoid bouncing the mutex when adding and deleting groups
Stop taking kv->lock mutex in kvm_vfio_update_coherency() and instead call it with this mutex held: the callers of the function usually already have it taken (and released) before calling kvm_vfio_update_coherency(). This avoid bouncing the lock up and down. The exception is kvm_vfio_release() where we do not take the lock, but it is being executed when the very last reference to kvm_device is being dropped, so there are no concerns about concurrency. Suggested-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Alex Williamson <alex.williamson@redhat.com> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> Link: https://lore.kernel.org/r/20230714224538.404793-2-dmitry.torokhov@gmail.com Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Diffstat (limited to 'virt/kvm')
-rw-r--r--virt/kvm/vfio.c26
1 files changed, 9 insertions, 17 deletions
diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index 59945f6001f4..ca24ce120906 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -123,8 +123,6 @@ static void kvm_vfio_update_coherency(struct kvm_device *dev)
bool noncoherent = false;
struct kvm_vfio_file *kvf;
- mutex_lock(&kv->lock);
-
list_for_each_entry(kvf, &kv->file_list, node) {
if (!kvm_vfio_file_enforced_coherent(kvf->file)) {
noncoherent = true;
@@ -140,8 +138,6 @@ static void kvm_vfio_update_coherency(struct kvm_device *dev)
else
kvm_arch_unregister_noncoherent_dma(dev->kvm);
}
-
- mutex_unlock(&kv->lock);
}
static int kvm_vfio_file_add(struct kvm_device *dev, unsigned int fd)
@@ -149,7 +145,7 @@ static int kvm_vfio_file_add(struct kvm_device *dev, unsigned int fd)
struct kvm_vfio *kv = dev->private;
struct kvm_vfio_file *kvf;
struct file *filp;
- int ret;
+ int ret = 0;
filp = fget(fd);
if (!filp)
@@ -158,7 +154,7 @@ static int kvm_vfio_file_add(struct kvm_device *dev, unsigned int fd)
/* Ensure the FD is a vfio FD. */
if (!kvm_vfio_file_is_valid(filp)) {
ret = -EINVAL;
- goto err_fput;
+ goto out_fput;
}
mutex_lock(&kv->lock);
@@ -166,30 +162,26 @@ static int kvm_vfio_file_add(struct kvm_device *dev, unsigned int fd)
list_for_each_entry(kvf, &kv->file_list, node) {
if (kvf->file == filp) {
ret = -EEXIST;
- goto err_unlock;
+ goto out_unlock;
}
}
kvf = kzalloc(sizeof(*kvf), GFP_KERNEL_ACCOUNT);
if (!kvf) {
ret = -ENOMEM;
- goto err_unlock;
+ goto out_unlock;
}
- kvf->file = filp;
+ kvf->file = get_file(filp);
list_add_tail(&kvf->node, &kv->file_list);
kvm_arch_start_assignment(dev->kvm);
kvm_vfio_file_set_kvm(kvf->file, dev->kvm);
-
- mutex_unlock(&kv->lock);
-
kvm_vfio_update_coherency(dev);
- return 0;
-err_unlock:
+out_unlock:
mutex_unlock(&kv->lock);
-err_fput:
+out_fput:
fput(filp);
return ret;
}
@@ -225,12 +217,12 @@ static int kvm_vfio_file_del(struct kvm_device *dev, unsigned int fd)
break;
}
+ kvm_vfio_update_coherency(dev);
+
mutex_unlock(&kv->lock);
fdput(f);
- kvm_vfio_update_coherency(dev);
-
return ret;
}