From: Alex Williamson <alex.williamson@redhat.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
cohuck@redhat.com, peterx@redhat.com
Subject: Re: [PATCH 1/3] vfio/type1: Support faulting PFNMAP vmas
Date: Mon, 4 May 2020 08:06:30 -0600 [thread overview]
Message-ID: <20200504080630.293f33e8@x1.home> (raw)
In-Reply-To: <20200501235033.GA19929@ziepe.ca>
On Fri, 1 May 2020 20:50:33 -0300
Jason Gunthorpe <jgg@ziepe.ca> 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@redhat.com>
> > 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
next prev parent reply other threads:[~2020-05-04 14:07 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-01 21:38 [PATCH 0/3] vfio-pci: Block user access to disabled device MMIO Alex Williamson
2020-05-01 21:39 ` [PATCH 1/3] vfio/type1: Support faulting PFNMAP vmas Alex Williamson
2020-05-01 23:50 ` Jason Gunthorpe
2020-05-04 14:06 ` Alex Williamson [this message]
2020-05-04 15:02 ` Jason Gunthorpe
2020-05-01 21:39 ` [PATCH 2/3] vfio-pci: Fault mmaps to enable vma tracking Alex Williamson
2020-05-01 23:25 ` Jason Gunthorpe
2020-05-04 14:20 ` Alex Williamson
2020-05-04 15:05 ` Jason Gunthorpe
2020-05-04 15:53 ` Alex Williamson
2020-05-01 21:39 ` [PATCH 3/3] vfio-pci: Invalidate mmaps and block MMIO access on disabled memory Alex Williamson
2020-05-01 23:48 ` Jason Gunthorpe
2020-05-04 18:26 ` Alex Williamson
2020-05-04 18:44 ` Jason Gunthorpe
2020-05-04 19:35 ` Alex Williamson
2020-05-04 20:01 ` Jason Gunthorpe
2020-05-05 17:12 ` Alex Williamson
2020-05-05 18:36 ` Jason Gunthorpe
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