From 73e2f19da50857a3488f44a7c9d874fed6fae533 Mon Sep 17 00:00:00 2001 From: Dmitry Torokhov Date: Fri, 14 Jul 2023 15:45:33 -0700 Subject: 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 Reviewed-by: Alex Williamson Signed-off-by: Dmitry Torokhov Reviewed-by: Kevin Tian Link: https://lore.kernel.org/r/20230714224538.404793-2-dmitry.torokhov@gmail.com Signed-off-by: Alex Williamson --- virt/kvm/vfio.c | 26 +++++++++----------------- 1 file changed, 9 insertions(+), 17 deletions(-) (limited to 'virt') 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; } -- cgit