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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Peter Xu <peterx@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	cohuck@redhat.com
Subject: Re: [PATCH v2 1/3] vfio/type1: Support faulting PFNMAP vmas
Date: Thu, 7 May 2020 20:54:21 -0300
Message-ID: <20200507235421.GK26002@ziepe.ca> (raw)
In-Reply-To: <20200507212443.GO228260@xz-x1>

On Thu, May 07, 2020 at 05:24:43PM -0400, Peter Xu wrote:
> On Tue, May 05, 2020 at 03:54:44PM -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;
> 
> Hi, Alex,
> 
> IIUC this retry is not needed too because fixup_user_fault() will guarantee the
> fault-in is done correctly with the valid PTE as long as ret==0, even if
> unlocked==true.

It is true, and today it is fine, but be careful when reworking this
to use notifiers as unlocked also means things like the vma pointer
are invalidated.

Jason

  parent reply index

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-05 21:54 [PATCH v2 0/3] vfio-pci: Block user access to disabled device MMIO Alex Williamson
2020-05-05 21:54 ` [PATCH v2 1/3] vfio/type1: Support faulting PFNMAP vmas Alex Williamson
2020-05-07 21:24   ` Peter Xu
2020-05-07 21:47     ` Alex Williamson
2020-05-07 23:54     ` Jason Gunthorpe [this message]
2020-05-08  2:19       ` Peter Xu
2020-05-08 12:10         ` Jason Gunthorpe
2020-05-08 14:30           ` Peter Xu
2020-05-08 15:05             ` Jason Gunthorpe
2020-05-08 15:42               ` Alex Williamson
2020-05-08 16:05                 ` Peter Xu
2020-05-08 18:39   ` Peter Xu
2020-05-05 21:54 ` [PATCH v2 2/3] vfio-pci: Fault mmaps to enable vma tracking Alex Williamson
2020-05-07 21:47   ` Peter Xu
2020-05-07 22:03     ` Alex Williamson
2020-05-07 22:22       ` Peter Xu
2020-05-07 23:56         ` Jason Gunthorpe
2020-05-08  2:16           ` Peter Xu
2020-05-08  6:44             ` Jason Wang
2020-05-08 14:27               ` Peter Xu
2020-05-08 12:08             ` Jason Gunthorpe
2020-05-08 14:26               ` Peter Xu
2020-05-05 21:55 ` [PATCH v2 3/3] vfio-pci: Invalidate mmaps and block MMIO access on disabled memory Alex Williamson
2020-05-22  2:39   ` Qian Cai
2020-05-22  4:18     ` Alex Williamson
2020-05-07 21:59 ` [PATCH v2 0/3] vfio-pci: Block user access to disabled device MMIO Peter Xu
2020-05-07 22:34   ` Alex Williamson
2020-05-08  2:31     ` Peter Xu

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