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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>
This commit is contained in:
Dmitry Torokhov 2023-07-14 15:45:33 -07:00 committed by Alex Williamson
parent 9e0f4f2918
commit 73e2f19da5
1 changed files with 9 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
virt/kvm/vfio.c
View File

@ -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;
}