From ddd89d0a059d8e9740c75a97e0efe9bf07ee51f9 Mon Sep 17 00:00:00 2001 From: Jason Wang Date: Fri, 29 May 2020 16:03:01 +0800 Subject: [PATCH] vhost_vdpa: support doorbell mapping via mmap Currently the doorbell is relayed via eventfd which may have significant overhead because of the cost of vmexits or syscall. This patch introduces mmap() based doorbell mapping which can eliminate the overhead caused by vmexit or syscall. To ease the userspace modeling of the doorbell layout (usually virtio-pci), this patch starts from a doorbell per page model. Vhost-vdpa only support the hardware doorbell that sit at the boundary of a page and does not share the page with other registers. Doorbell of each virtqueue must be mapped separately, pgoff is the index of the virtqueue. This allows userspace to map a subset of the doorbell which may be useful for the implementation of software assisted virtqueue (control vq) in the future. Signed-off-by: Jason Wang Link: https://lore.kernel.org/r/20200529080303.15449-5-jasowang@redhat.com Signed-off-by: Michael S. Tsirkin --- drivers/vhost/vdpa.c | 59 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c index f22bb316b8c4..3d163ec6fb28 100644 --- a/drivers/vhost/vdpa.c +++ b/drivers/vhost/vdpa.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include #include @@ -739,12 +740,70 @@ static int vhost_vdpa_release(struct inode *inode, struct file *filep) return 0; } +static vm_fault_t vhost_vdpa_fault(struct vm_fault *vmf) +{ + struct vhost_vdpa *v = vmf->vma->vm_file->private_data; + struct vdpa_device *vdpa = v->vdpa; + const struct vdpa_config_ops *ops = vdpa->config; + struct vdpa_notification_area notify; + struct vm_area_struct *vma = vmf->vma; + u16 index = vma->vm_pgoff; + + notify = ops->get_vq_notification(vdpa, index); + + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); + if (remap_pfn_range(vma, vmf->address & PAGE_MASK, + notify.addr >> PAGE_SHIFT, PAGE_SIZE, + vma->vm_page_prot)) + return VM_FAULT_SIGBUS; + + return VM_FAULT_NOPAGE; +} + +static const struct vm_operations_struct vhost_vdpa_vm_ops = { + .fault = vhost_vdpa_fault, +}; + +static int vhost_vdpa_mmap(struct file *file, struct vm_area_struct *vma) +{ + struct vhost_vdpa *v = vma->vm_file->private_data; + struct vdpa_device *vdpa = v->vdpa; + const struct vdpa_config_ops *ops = vdpa->config; + struct vdpa_notification_area notify; + int index = vma->vm_pgoff; + + if (vma->vm_end - vma->vm_start != PAGE_SIZE) + return -EINVAL; + if ((vma->vm_flags & VM_SHARED) == 0) + return -EINVAL; + if (vma->vm_flags & VM_READ) + return -EINVAL; + if (index > 65535) + return -EINVAL; + if (!ops->get_vq_notification) + return -ENOTSUPP; + + /* To be safe and easily modelled by userspace, We only + * support the doorbell which sits on the page boundary and + * does not share the page with other registers. + */ + notify = ops->get_vq_notification(vdpa, index); + if (notify.addr & (PAGE_SIZE - 1)) + return -EINVAL; + if (vma->vm_end - vma->vm_start != notify.size) + return -ENOTSUPP; + + vma->vm_ops = &vhost_vdpa_vm_ops; + return 0; +} + static const struct file_operations vhost_vdpa_fops = { .owner = THIS_MODULE, .open = vhost_vdpa_open, .release = vhost_vdpa_release, .write_iter = vhost_vdpa_chr_write_iter, .unlocked_ioctl = vhost_vdpa_unlocked_ioctl, + .mmap = vhost_vdpa_mmap, .compat_ioctl = compat_ptr_ioctl, };