Hi Keqian, Peter,
On 2020/12/15 15:23, zhukeqian wrote:
On 2020/12/14 23:36, Peter Xu wrote:
On Mon, Dec 14, 2020 at 10:14:11AM +0800, zhukeqian wrote:
[...]
Though indeed I must confess I don't know how it worked in general when host
page size != target page size, at least for migration. For example, I believe
kvm dirty logging is host page size based, though migration should be migrating
pages in guest page size granule when it spots a dirty bit set.
[1]
Hi Peter,
Keqian,
OTOH I'm more worried on the other question on how we handle guest psize !=
host psize case for migration now...
I think it does not matter when guest_psize != host_psize, as we only need to
interact with
stage2 page tables during migration. Stage2 is enough to tracking guest dirty
memory, and even
if guest close stage1, we also can do a successful migration.
I don't know why 2-stage matters here, since I believe KVM can track dirty
pages either using two dimentional paging or shadowing, however it's always
done in host small page size. The question I'm confused is there seems to have
a size mismatch between qemu migration and what kvm does [1]. For example, how
migration works on ARM64 where host has psize==4K while guest has psize=64K.
Hi Peter,
OK, I got it ;-) Do you mean qemu_real_host_page_size != TARGET_PAGE_SIZE?
After my analysis, I see that when qemu_real_host_page_size != TARGET_PAGE_SIZE,
there are some problems indeed. I have send out some patches, please check
whether they solve this
problem, thanks!
Now I see what your concern is :) Thanks both for the explanation and
the further fix!
Zenghui
