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Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots
From: |
David Hildenbrand |
Subject: |
Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots |
Date: |
Thu, 11 Feb 2021 22:09:58 +0100 |
> Am 11.02.2021 um 22:05 schrieb Peter Xu <peterx@redhat.com>:
>
> 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..
The issue is when the discard happened before starting the snapshot.
Write-protection won‘t work and the zeroed content won‘t be retained in the
snapshot.
>
> 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.
Yes, but other issue.
>
> 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, 2021/02/11
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots,
David Hildenbrand <=
- 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
- Re: [PATCH v13 0/5] UFFD write-tracking migration/snapshots, Peter Xu, 2021/02/19