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Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots
From: |
Peter Xu |
Subject: |
Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots |
Date: |
Thu, 11 Feb 2021 16:05:49 -0500 |
On Thu, Feb 11, 2021 at 09:44:07PM +0100, David Hildenbrand wrote:
> Let‘s take a look at init-on-free.
>
> The guest zeroes a page and puts it onto a buddy freelist. Free page
> reporting code takes it off that list and reports it to the hypervisor. The
> hypervisor discards the physical page and tells the guest he‘s done
> processing the page. The guest re-places the page onto the free page list.
>
> From that point on, the page can be re-allocated inside the guest and is
> assumed to be zero. On access, a fresh (zeroed) page is populated by the
> hypervisor. The guest won‘t re-zero the page, as it has the guarantee (from
> free page reporting) that the page remained zero.
>
> Write-protecting the unpopulated page won‘t work as discussed.
IMHO no matter if it's init_on_alloc or init_on_free or both, as long as it's
inited in some way then it means the guest OS wrote to it. Then wr-protect
will work..
MADV_DONTNEED during live snapshot seems to be a separate topic as you
mentioned in the other thread. For that, I agree we'd better simply let
virtio_balloon_inhibited() to return true for live snapshot too just like
postcopy.
Thanks,
--
Peter Xu
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, (continued)
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Andrey Gruzdev, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Peter Xu, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Andrey Gruzdev, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, David Hildenbrand, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Peter Xu, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, David Hildenbrand, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots,
Peter Xu <=
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, David Hildenbrand, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Peter Xu, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, David Hildenbrand, 2021/02/12
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Peter Xu, 2021/02/12
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Andrey Gruzdev, 2021/02/13
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, David Hildenbrand, 2021/02/13
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Peter Xu, 2021/02/16
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, David Hildenbrand, 2021/02/17
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Andrey Gruzdev, 2021/02/19
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, David Hildenbrand, 2021/02/19