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[Qemu-devel] vhost, iova, and dirty page tracking
From: |
Tian, Kevin |
Subject: |
[Qemu-devel] vhost, iova, and dirty page tracking |
Date: |
Mon, 16 Sep 2019 01:51:46 +0000 |
Hi, Jason
We had a discussion about dirty page tracking in VFIO, when vIOMMU
is enabled:
https://lists.nongnu.org/archive/html/qemu-devel/2019-09/msg02690.html
It's actually a similar model as vhost - Qemu cannot interpose the fast-path
DMAs thus relies on the kernel part to track and report dirty page information.
Currently Qemu tracks dirty pages in GFN level, thus demanding a translation
from IOVA to GPA. Then the open in our discussion is where this translation
should happen. Doing the translation in kernel implies a device iotlb flavor,
which is what vhost implements today. It requires potentially large tracking
structures in the host kernel, but leveraging the existing log_sync flow in
Qemu.
On the other hand, Qemu may perform log_sync for every removal of IOVA
mapping and then do the translation itself, then avoiding the GPA awareness
in the kernel side. It needs some change to current Qemu log-sync flow, and
may bring more overhead if IOVA is frequently unmapped.
So we'd like to hear about your opinions, especially about how you came
down to the current iotlb approach for vhost.
p.s. Alex's comment is also copied here from original thread.
> So vhost must then be configuring a listener across system memory
> rather than only against the device AddressSpace like we do in vfio,
> such that it get's log_sync() callbacks for the actual GPA space rather
> than only the IOVA space. OTOH, QEMU could understand that the device
> AddressSpace has a translate function and apply the IOVA dirty bits to
> the system memory AddressSpace. Wouldn't it make more sense for
> QEMU
> to perform a log_sync() prior to removing a MemoryRegionSection within
> an AddressSpace and update the GPA rather than pushing GPA awareness
> and potentially large tracking structures into the host kernel?
Thanks
Kevin
- [Qemu-devel] vhost, iova, and dirty page tracking,
Tian, Kevin <=
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Jason Wang, 2019/09/16
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Tian, Kevin, 2019/09/17
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Jason Wang, 2019/09/17
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Tian, Kevin, 2019/09/17
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Jason Wang, 2019/09/18
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Tian, Kevin, 2019/09/18
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Tian, Kevin, 2019/09/18
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Jason Wang, 2019/09/18
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Yan Zhao, 2019/09/19
- Re: [Qemu-devel] vhost, iova, and dirty page tracking, Jason Wang, 2019/09/19