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

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Date:   Sat, 23 May 2020 15:34:17 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        cohuck@...hat.com, jgg@...pe.ca, cai@....pw
Subject: Re: [PATCH v3 3/3] vfio-pci: Invalidate mmaps and block MMIO access
 on disabled memory

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