On Fri, 1 May 2020 20:50:33 -0300
Jason Gunthorpe <jgg@xxxxxxxx> wrote:
> On Fri, May 01, 2020 at 03:39:08PM -0600, Alex Williamson wrote:
> > With conversion to follow_pfn(), DMA mapping a PFNMAP range depends on
> > the range being faulted into the vma. Add support to manually provide
> > that, in the same way as done on KVM with hva_to_pfn_remapped().
> >
> > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > drivers/vfio/vfio_iommu_type1.c | 36 +++++++++++++++++++++++++++++++++---
> > 1 file changed, 33 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index cc1d64765ce7..4a4cb7cd86b2 100644
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -317,6 +317,32 @@ static int put_pfn(unsigned long pfn, int prot)
> > return 0;
> > }
> >
> > +static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
> > + unsigned long vaddr, unsigned long *pfn,
> > + bool write_fault)
> > +{
> > + int ret;
> > +
> > + ret = follow_pfn(vma, vaddr, pfn);
> > + if (ret) {
> > + bool unlocked = false;
> > +
> > + ret = fixup_user_fault(NULL, mm, vaddr,
> > + FAULT_FLAG_REMOTE |
> > + (write_fault ? FAULT_FLAG_WRITE : 0),
> > + &unlocked);
> > + if (unlocked)
> > + return -EAGAIN;
> > +
> > + if (ret)
> > + return ret;
> > +
> > + ret = follow_pfn(vma, vaddr, pfn);
> > + }
> > +
> > + return ret;
> > +}
> > +
> > static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> > int prot, unsigned long *pfn)
> > {
> > @@ -339,12 +365,16 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> >
> > vaddr = untagged_addr(vaddr);
> >
> > +retry:
> > vma = find_vma_intersection(mm, vaddr, vaddr + 1);
> >
> > if (vma && vma->vm_flags & VM_PFNMAP) {
> > - if (!follow_pfn(vma, vaddr, pfn) &&
> > - is_invalid_reserved_pfn(*pfn))
> > - ret = 0;
> > + ret = follow_fault_pfn(vma, mm, vaddr, pfn, prot & IOMMU_WRITE);
> > + if (ret == -EAGAIN)
> > + goto retry;
> > +
> > + if (!ret && !is_invalid_reserved_pfn(*pfn))
> > + ret = -EFAULT;
>
> I suggest checking vma->vm_ops == &vfio_pci_mmap_ops and adding a
> comment that this is racy and needs to be fixed up. The ops check
> makes this only used by other vfio bars and should prevent some
> abuses of this hacky thing
We can't do that, vfio-pci is only one bus driver within the vfio
ecosystem.
> However, I wonder if this chould just link itself into the
> vma->private data so that when the vfio that owns the bar goes away,
> so does the iommu mapping?
I don't really see why we wouldn't use mmu notifiers so that the vfio
iommu backend and vfio bus driver remain independent.
> I feel like this patch set is not complete unless it also handles the
> shootdown of this path too?
It would be nice to solve both issues and I'll start working on the mmu
notifier side of things, but this series does solve a real issue on
its own and we're not changing the iommu mapping behavior here. Thanks,
Alex
