From: Jason Gunthorpe <jgg@nvidia.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Zeng Tao <prime.zeng@hisilicon.com>,
linuxarm@huawei.com, Cornelia Huck <cohuck@redhat.com>,
Kevin Tian <kevin.tian@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Xu <peterx@redhat.com>,
Giovanni Cabiddu <giovanni.cabiddu@intel.com>,
Michel Lespinasse <walken@google.com>,
Jann Horn <jannh@google.com>, Max Gurtovoy <mgurtovoy@nvidia.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vfio/pci: make the vfio_pci_mmap_fault reentrant
Date: Mon, 8 Mar 2021 19:43:53 -0400 [thread overview]
Message-ID: <20210308234353.GB4247@nvidia.com> (raw)
In-Reply-To: <20210308132106.49da42e2@omen.home.shazbot.org>
On Mon, Mar 08, 2021 at 01:21:06PM -0700, Alex Williamson wrote:
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index 65e7e6b..6928c37 100644
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -1613,6 +1613,7 @@ 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;
> > + unsigned long pfn;
> >
> > mutex_lock(&vdev->vma_lock);
> > down_read(&vdev->memory_lock);
> > @@ -1623,18 +1624,23 @@ static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf)
> > goto up_out;
> > }
> >
> > - if (__vfio_pci_add_vma(vdev, vma)) {
> > - ret = VM_FAULT_OOM;
> > + if (!follow_pfn(vma, vma->vm_start, &pfn)) {
> > mutex_unlock(&vdev->vma_lock);
> > goto up_out;
Gah, no new follow_pfn users please we are trying to delete this
stuff..
I believe the right fix is to change the fault handler to use
vmf_insert_pfn_prot() which has all the right locking/etc
The
> I'm surprised that it's left to the fault handler to provide this
> serialization, is this because we're filling the entire vma rather than
> only the faulting page?
I think it is because remap_pfn is not intended to be called from a
fault handler. The fault handler APIs seem to be named vmf_* ..
If you want to use remap API it has to be done and managed outside the
fault handler. Ie when the MMIO transitions from valid->invalid vfio-pci
wipes the address space, when it transitions from invalid->valid it
calls remap_pfn. vfio-pci provides its own locking to protect these
state transitions. fault simply always triggers sigbus
I recall we discussed this design when you made the original patches
but I don't completely recall why it ended this way, however I think
the reason might disappear after the address_space conversion in your
other series.
Jason
prev parent reply other threads:[~2021-03-08 23:44 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 11:11 [PATCH] vfio/pci: make the vfio_pci_mmap_fault reentrant Zeng Tao
2021-03-08 20:21 ` Alex Williamson
2021-03-08 22:56 ` Peter Xu
2021-03-09 3:49 ` 答复: " Zengtao (B)
2021-03-09 12:46 ` Jason Gunthorpe
2021-03-09 15:29 ` Alex Williamson
2021-03-09 16:40 ` Jason Gunthorpe
2021-03-09 18:47 ` Peter Xu
2021-03-09 19:26 ` Alex Williamson
2021-03-09 19:48 ` Peter Xu
2021-03-09 20:11 ` Alex Williamson
2021-03-09 21:00 ` Peter Xu
2021-03-09 21:43 ` Alex Williamson
2021-03-09 19:56 ` Alex Williamson
2021-03-09 23:45 ` Jason Gunthorpe
2021-03-10 6:23 ` Alex Williamson
2021-03-09 23:41 ` Jason Gunthorpe
2021-03-10 6:08 ` Alex Williamson
2021-03-11 3:32 ` 答复: " Zengtao (B)
2021-03-08 23:43 ` Jason Gunthorpe [this message]
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