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Date: Thu, 1 Feb 2018 19:05:03 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v4 0/6] nvdimm: support MAP_SYNC for
 memory-backend-file
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To: Dan Williams <dan.j.williams@intel.com>
Cc: Qemu Developers <qemu-devel@nongnu.org>, Eduardo Habkost <ehabkost@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, dgilbert@redhat.com, Xiao Guangrong <xiaoguangrong.eric@gmail.com>, Stefan Hajnoczi <stefanha@redhat.com>, Alex Williamson <alex.williamson@redhat.com>

On Wed, Jan 31, 2018 at 07:02:27PM -0800, Dan Williams wrote:
> > Another question is how a user-space application (e.g., QEMU) knows
> > whether it's safe to mmap a file on the DAX file system?
> 
> I think we fix vaddr_get_pfn() to start failing for DAX mappings
> unless/until we can add a "with lease" mechanism. Userspace will know
> when it is safe again when vfio stops failing.

I read some of the discussion around that but could not figure out what
exactly does happen if a file is truncated by a malicious userspace.
Could you let me know pls? Thanks!

-- 
MST