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[Qemu-devel] Re: Re: Live migration protocol, device features, ABIs and
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] Re: Re: Live migration protocol, device features, ABIs and other beasts |
Date: |
Tue, 24 Nov 2009 16:26:49 +0200 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On Mon, Nov 23, 2009 at 09:12:15AM -0600, Anthony Liguori wrote:
> Eduardo Habkost wrote:
>> The pvclock MSRs are an example: if the guest is not using pvclock, not
>> restoring the MSRs won't make any difference. Strictly speaking, not
>> migrating them is wrong, but the user may argue that they know it won't
>> impact their guest OS, and that they want to take the risk.
>
> Once you start dealing with issues of risk vs. benefit, it's a policy
> and belongs in the management layer.
>
> We don't make risk vs. benefit assessments in qemu. We defer those
> types of decisions.
>
> Today, we only succeed migration when we know it will be successful. We
> could allow a management tool to override this check such that it could
> implement such a policy. But that's a really dangerous option to offer.
>
>> Also, on the pvclock MSR case (and probably others), any argument
>> against doing backward migration would also be valid against doing
>> forward migration when the source process doesn't have the fix yet,
>> because the pvclock MSRs won't be migrated anyway. Forward migration is
>> as broken as backward migration, but we don't prevent migration on that
>> direction.
>>
>
> A bug that is visible to a guest is no longer a bug, but a feature that
> has to be supported for as long as that release is supported. If we
> feel that it's too dangerous of a bug, then we need to fail gracefully
> and refuse to load that state on any other system forcing a proper
> shutdown/startup for migration to a new version of qemu.
>
> For the purposes of compatibility, it is something that we have to
> preserve. In this case, you're introducing two MSRs that are readable
> and writable by a guest. If you migrate all of the sudden you lose that
> MSRs content. You cannot have live migration cause an MSR to disappear
> regardless of what the purpose of that MSR is.
>
> Regards,
>
> Anthony Liguori
Same with having MSRs appear, surely?
--
MST
- [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, (continued)
- Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Eduardo Habkost, 2009/11/23
- [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Michael S. Tsirkin, 2009/11/24
- Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Eduardo Habkost, 2009/11/23
- Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Paolo Bonzini, 2009/11/23
- Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Anthony Liguori, 2009/11/23
- Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Eduardo Habkost, 2009/11/23
- Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Eduardo Habkost, 2009/11/23
- Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Anthony Liguori, 2009/11/23
- [Qemu-devel] Re: Re: Live migration protocol, device features, ABIs and other beasts,
Michael S. Tsirkin <=
- Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Anthony Liguori, 2009/11/23
- [Qemu-devel] Re: Re: Live migration protocol, device features, ABIs and other beasts, Michael S. Tsirkin, 2009/11/24
- [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Anthony Liguori, 2009/11/24
- [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Michael S. Tsirkin, 2009/11/24
- Message not available
- [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Michael S. Tsirkin, 2009/11/25
- [Qemu-devel] Re: Re: Live migration protocol, device features, ABIs and other beasts, Michael S. Tsirkin, 2009/11/24
- Re: [Qemu-devel] Re: Re: Live migration protocol, device features, ABIs and other beasts, Paul Brook, 2009/11/24
- [Qemu-devel] Re: Re: Re: Live migration protocol, device features, ABIs and other beasts, Michael S. Tsirkin, 2009/11/24
- [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Paul Brook, 2009/11/24
- [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts, Michael S. Tsirkin, 2009/11/24