Re: [PATCH V3 0/9] vfio virtual address update

[Steven Sistare <steven.sistare@oracle.com>]

On 1/29/2021 4:55 PM, Alex Williamson wrote:
> On Fri, 29 Jan 2021 08:54:03 -0800
> Steve Sistare <steven.sistare@oracle.com> 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 1-3 define and implement the flag to unmap all ranges.
>> Patches 4-6 define and implement the flags to update vaddr.
>> Patches 7-9 add blocking to complete the implementation.
> 
> Hi Steve,
> 
> It looks pretty good to me, but I have some nit-picky comments that
> I'll follow-up with on the individual patches.  However, I've made the
> changes I suggest in a branch that you can find here:
> 
> git://github.com/awilliam/linux-vfio.git vaddr-v3
> 
> If the changes look ok, just send me an ack, I don't want to attribute
> something to you that you don't approve of.  Thanks,

All changes look good, thanks!  
Do you need anything more from me on this patch series?

- Steve

>> Changes in V2:
>>  - 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
>>
>> Changes in V3:
>>  - add vaddr_invalid_count to fix pin_pages race with unmap
>>  - refactor the wait helper functions
>>  - traverse dma entries more efficiently in unmap
>>  - check unmap flag conflicts more explicitly
>>  - rename some local variables and functions
>>
>> Steve Sistare (9):
>>   vfio: option to unmap all
>>   vfio/type1: unmap cleanup
>>   vfio/type1: implement unmap all
>>   vfio: interfaces to update vaddr
>>   vfio/type1: massage unmap iteration
>>   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 | 251 +++++++++++++++++++++++++++++++++++-----
>>  include/linux/vfio.h            |   5 +
>>  include/uapi/linux/vfio.h       |  27 +++++
>>  4 files changed, 256 insertions(+), 32 deletions(-)
>>
>