Re: [PATCH V2 0/9] vfio virtual address update

From: Alex Williamson <alex.williamson@redhat.com>
To: Steven Sistare <steven.sistare@oracle.com>
Cc: Cornelia Huck <cohuck@redhat.com>,
	Kirti Wankhede <kwankhede@nvidia.com>,
	kvm@vger.kernel.org
Subject: Re: [PATCH V2 0/9] vfio virtual address update
Date: Fri, 29 Jan 2021 10:05:41 -0700	[thread overview]
Message-ID: <20210129100541.5b0c3d0f@omen.home.shazbot.org> (raw)
In-Reply-To: <55725169-de0d-4019-f96c-ded20dfde0d7@oracle.com>

On Fri, 29 Jan 2021 10:48:10 -0500
Steven Sistare <steven.sistare@oracle.com> wrote:

> Hi Alex, thanks for the feedback on V2.  Any more comments before I submit V3? 

Nope, I'm ok with your proposals.  Thanks,

Alex

> On 1/19/2021 12:48 PM, Steve Sistare wrote:
> > Add interfaces that allow the underlying memory object of an iova range
> > to be mapped to a new virtual address in the host process:
> > 
> >   - VFIO_DMA_UNMAP_FLAG_VADDR for VFIO_IOMMU_UNMAP_DMA
> >   - VFIO_DMA_MAP_FLAG_VADDR flag for VFIO_IOMMU_MAP_DMA
> >   - VFIO_UPDATE_VADDR for VFIO_CHECK_EXTENSION
> >   - VFIO_DMA_UNMAP_FLAG_ALL for VFIO_IOMMU_UNMAP_DMA
> >   - VFIO_UNMAP_ALL for VFIO_CHECK_EXTENSION
> > 
> > Unmap-vaddr invalidates the host virtual address in an iova range and blocks
> > vfio translation of host virtual addresses, but DMA to already-mapped pages
> > continues.  Map-vaddr updates the base VA and resumes translation.  The
> > implementation supports iommu type1 and mediated devices.  Unmap-all allows
> > all ranges to be unmapped or invalidated in a single ioctl, which simplifies
> > userland code.
> > 
> > This functionality is necessary for live update, in which a host process
> > such as qemu exec's an updated version of itself, while preserving its
> > guest and vfio devices.  The process blocks vfio VA translation, exec's
> > its new self, mmap's the memory object(s) underlying vfio object, updates
> > the VA, and unblocks translation.  For a working example that uses these
> > new interfaces, see the QEMU patch series "[PATCH V2] Live Update" at
> > https://lore.kernel.org/qemu-devel/1609861330-129855-1-git-send-email-steven.sistare@oracle.com
> > 
> > Patches 1-4 define and implement the flag to unmap all ranges.
> > Patches 5-6 define and implement the flags to update vaddr.
> > Patches 7-9 add blocking to complete the implementation.
> > 
> > Changes from V1:
> >  - define a flag for unmap all instead of special range values
> >  - define the VFIO_UNMAP_ALL extension
> >  - forbid the combination of unmap-all and get-dirty-bitmap
> >  - unwind in unmap on vaddr error
> >  - add a new function to find first dma in a range instead of modifying
> >    an existing function
> >  - change names of update flags
> >  - fix concurrency bugs due to iommu lock being dropped
> >  - call down from from vfio to a new backend interface instead of up from
> >    driver to detect container close
> >  - use wait/wake instead of sleep and polling
> >  - refine the uapi specification
> >  - split patches into vfio vs type1
> > 
> > Steve Sistare (9):
> >   vfio: option to unmap all
> >   vfio/type1: find first dma
> >   vfio/type1: unmap cleanup
> >   vfio/type1: implement unmap all
> >   vfio: interfaces to update vaddr
> >   vfio/type1: implement interfaces to update vaddr
> >   vfio: iommu driver notify callback
> >   vfio/type1: implement notify callback
> >   vfio/type1: block on invalid vaddr
> > 
> >  drivers/vfio/vfio.c             |   5 +
> >  drivers/vfio/vfio_iommu_type1.c | 229 ++++++++++++++++++++++++++++++++++------
> >  include/linux/vfio.h            |   5 +
> >  include/uapi/linux/vfio.h       |  27 +++++
> >  4 files changed, 231 insertions(+), 35 deletions(-)
> >   
> 