Re: [PATCH v3 3/3] vfio-pci: Invalidate mmaps and block MMIO access on disabled memory

Peter Xu
2020-05-23T19:34:25Z

Hi, Alex,

On Fri, May 22, 2020 at 01:17:43PM -0600, Alex Williamson wrote:
> @@ -1346,15 +1526,32 @@ static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf)
> {
> struct vm_area_struct *vma = vmf->vma;
> struct vfio_pci_device *vdev = vma->vm_private_data;
> + vm_fault_t ret = VM_FAULT_NOPAGE;
> +
> + mutex_lock(&vdev->vma_lock);
> + down_read(&vdev->memory_lock);

I remembered to have seen the fault() handling FAULT_FLAG_RETRY_NOWAIT at least
in the very first version, but it's not here any more... Could I ask what's
the reason behind? I probably have missed something along with the versions,
I'm just not sure whether e.g. this would potentially block a GUP caller even
if it's with FOLL_NOWAIT.

Side note: Another thing I thought about when reading this patch - there seems
to have quite some possibility that the VFIO_DEVICE_PCI_HOT_RESET ioctl will
start to return -EBUSY now. Not a problem for this series, but maybe we should
rememeber to let the userspace handle -EBUSY properly as follow up too, since I
saw QEMU seemed to not handle -EBUSY for host reset path right now.

Thanks,

--
Peter Xu