On 7/15/2024 10:38 AM, Michael S. Tsirkin wrote:
On Mon, Jul 15, 2024 at 10:29:26AM -0400, Steven Sistare wrote:
On 7/15/2024 5:07 AM, Michael S. Tsirkin wrote:
On Fri, Jul 12, 2024 at 06:18:49AM -0700, Steve Sistare wrote:
Add an ioctl to transfer file descriptor ownership and pinned memory
accounting from one process to another.
This is more efficient than VHOST_RESET_OWNER followed by VHOST_SET_OWNER,
as that would unpin all physical pages, requiring them to be repinned in
the new process. That would cost multiple seconds for large memories, and
be incurred during a virtual machine's pause time during live update.
Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
Please, we just need to switch to use iommufd for pinning.
Piling up all these hacks gets us nowhere.
I am working on iommufd kernel interfaces and QEMU changes. But who is working
on iommufd support for vdpa? If no one, or not for years, then adding these
small interfaces to vdpa plugs a signficant gap in live update coverage.
FWIW, the iommufd interfaces for live update will look much the same: change owner
and pinned memory accounting, and update virtual addresses. So adding that to vdpa
will not make it look like an odd duck.
- Steve
I think that no one is working on it - Cindy posted some rfcs in January
("vhost-vdpa: add support for iommufd"). Feel free to pick that up.
What you described is just more of a reason not to duplicate this code.
And it's always the same: a small extension here, a small extension there.
If you can make do with existing kernel interfaces, fine,
one can argue that userspace code is useful to support existing kernels.
Respectfully, I will not be volunteering to take that on. My work funnel to
deliver live update is already too wide. I hope that folks on this distribution
find the functionality interesting and useful enough to continue to review this
current proposal.
- Steve
