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    SubjectRe: [RFC PATCH v4 5/7] vfio-pci: Allow to mmap sub-page MMIO BARs if the mmio page is exclusive
    On Mon,  7 Mar 2016 15:48:36 +0800
    Yongji Xie <xyjxie@linux.vnet.ibm.com> wrote:

    > Current vfio-pci implementation disallows to mmap
    > sub-page(size < PAGE_SIZE) MMIO BARs because these BARs' mmio
    > page may be shared with other BARs.
    >
    > But we should allow to mmap these sub-page MMIO BARs if PCI
    > resource allocator can make sure these BARs' mmio page will
    > not be shared with other BARs.
    >
    > Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>
    > ---
    > drivers/vfio/pci/vfio_pci.c | 7 ++++++-
    > 1 file changed, 6 insertions(+), 1 deletion(-)
    >
    > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
    > index 1ce1d36..49d7a69 100644
    > --- a/drivers/vfio/pci/vfio_pci.c
    > +++ b/drivers/vfio/pci/vfio_pci.c
    > @@ -589,7 +589,8 @@ static long vfio_pci_ioctl(void *device_data,
    > VFIO_REGION_INFO_FLAG_WRITE;
    > if (IS_ENABLED(CONFIG_VFIO_PCI_MMAP) &&
    > pci_resource_flags(pdev, info.index) &
    > - IORESOURCE_MEM && info.size >= PAGE_SIZE) {
    > + IORESOURCE_MEM && !pci_resources_share_page(pdev,
    > + info.index)) {

    this would be a preferable line wrap:

    IORESOURCE_MEM &&
    !pci_resources_share_page(pdev, info.index)) {

    > info.flags |= VFIO_REGION_INFO_FLAG_MMAP;
    > if (info.index == vdev->msix_bar) {
    > ret = msix_sparse_mmap_cap(vdev, &caps);
    > @@ -1016,6 +1017,10 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma)
    > return -EINVAL;
    >
    > phys_len = pci_resource_len(pdev, index);
    > +
    > + if (!pci_resources_share_page(pdev, index))
    > + phys_len = PAGE_ALIGN(phys_len);
    > +
    > req_len = vma->vm_end - vma->vm_start;
    > pgoff = vma->vm_pgoff &
    > ((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);

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