From: Liran Alon <liran.alon@oracle.com> To: "\"Daniel P. Berrangé\"" <berrange@redhat.com> Cc: ehabkost@redhat.com, kvm@vger.kernel.org, mtosatti@redhat.com, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>, rth@twiddle.net, jmattson@google.com Subject: Re: [QEMU PATCH v2 0/2]: KVM: i386: Add support for save and restore nested state Date: Tue, 13 Nov 2018 02:00:22 +0200 [thread overview] Message-ID: <04AB82C1-F0AC-4BDB-A132-D39A49EA0A9A@oracle.com> (raw) In-Reply-To: <20181112165437.GW3602@redhat.com> > On 12 Nov 2018, at 18:54, Daniel P. Berrangé <berrange@redhat.com> wrote: > > On Mon, Nov 12, 2018 at 04:50:54PM +0000, Dr. David Alan Gilbert wrote: >> * Daniel P. Berrangé (berrange@redhat.com) wrote: >>> On Sun, Nov 04, 2018 at 11:19:57PM +0100, Paolo Bonzini wrote: >>>> On 02/11/2018 17:54, Daniel P. Berrangé wrote: >>>>> We have usually followed a rule that new machine types must not >>>>> affect runability of a VM on a host. IOW new machine types should >>>>> not introduce dependancies on specific kernels, or hardware features >>>>> such as CPU flags. >>>> >>>>> Anything that requires a new kernel feature thus ought to be an >>>>> opt-in config tunable on the CLI, separate from machine type >>>>> choice. >>>> >>>> Unless someone tinkered with the module parameters, they could not even >>>> use nested virtualization before 4.20. So for everyone else, "-cpu >>>> ...,+vmx" does count as an "opt-in config tunable on the CLI" that >>>> requires 4.20. >>>> >>>> For those that did tinker with module parameters, we can grandfather in >>>> the old machine types, so that they can use nested virtualization with >>>> no live migration support. For those that did not, however, I don't >>>> think it makes sense to say "oh by the way I really want to be able to >>>> migrate this VM" on the command line, or even worse on the monitor. >>> >>> IIUC, 4.20 is only required from POV of migration state. Is it thus >>> possible to just register a migration blocker if QEMU is launched >>> on a host with kernel < 4.20. >>> >>> Migration has always been busted historically, so those people using >>> nested VMX already won't be hurt by not having ability to live migrate >>> their VM, but could otherwise continue using them without being forced >>> to upgrade their kernel to fix a feature they're not even using. >> >> Yes, although I am a bit worried we might have a population of users >> that: >> a) Have enabled nesting >> b) Run VMs with vmx enabled > > >> c) Don't normally actually run nested guests >> d) Currently happily migrate. > > True, and (b) would include anyone using libvirt's host-model CPU. So if > you enabled nesting, have host-model for all guests, but only use nesting > in one of the guests, you'd be doomed. > > Is it possible for QEMU to determine if there are nested guests running or > not and conditionally block migration appropriately to ensure safety ? Only if kernel supports KVM_CAP_NESTED_STATE. See my reply to Dave in this thread. -Liran > > > Regards, > Daniel > -- > |: https://urldefense.proofpoint.com/v2/url?u=https-3A__berrange.com&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=DIzWfmRGWO1b6hzL9NRbIt41fiFcnPt0MC8917u4Qv0&e= -o- https://urldefense.proofpoint.com/v2/url?u=https-3A__www.flickr.com_photos_dberrange&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=CjA-joyt2Y9t5B4YzIiupfY8EEO58m4vbmnd45adzFI&e= :| > |: https://urldefense.proofpoint.com/v2/url?u=https-3A__libvirt.org&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=tD05tikOHMJhh_EeZ2Esoxb0oku3MPFmj-S2YHdUGm0&e= -o- https://urldefense.proofpoint.com/v2/url?u=https-3A__fstop138.berrange.com&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=YAh1WAoXQKEB6hkMmG6ZnJQETOFnq6eqQLmJokME80A&e= :| > |: https://urldefense.proofpoint.com/v2/url?u=https-3A__entangle-2Dphoto.org&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=90Mm1Qb-SHe8P63xwGp6gzMU1I5DEW6YX0ttG6TL_7g&e= -o- https://urldefense.proofpoint.com/v2/url?u=https-3A__www.instagram.com_dberrange&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=l4NrrDdRzPClvYQdxQdfIW0geHPWcukeyOGX8QapwYA&e= :|
WARNING: multiple messages have this Message-ID (diff)
From: Liran Alon <liran.alon@oracle.com> To: "\"Daniel P. Berrangé\"" <berrange@redhat.com> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, jmattson@google.com, ehabkost@redhat.com, kvm@vger.kernel.org, mtosatti@redhat.com, qemu-devel@nongnu.org, rth@twiddle.net Subject: Re: [Qemu-devel] [QEMU PATCH v2 0/2]: KVM: i386: Add support for save and restore nested state Date: Tue, 13 Nov 2018 02:00:22 +0200 [thread overview] Message-ID: <04AB82C1-F0AC-4BDB-A132-D39A49EA0A9A@oracle.com> (raw) In-Reply-To: <20181112165437.GW3602@redhat.com> > On 12 Nov 2018, at 18:54, Daniel P. Berrangé <berrange@redhat.com> wrote: > > On Mon, Nov 12, 2018 at 04:50:54PM +0000, Dr. David Alan Gilbert wrote: >> * Daniel P. Berrangé (berrange@redhat.com) wrote: >>> On Sun, Nov 04, 2018 at 11:19:57PM +0100, Paolo Bonzini wrote: >>>> On 02/11/2018 17:54, Daniel P. Berrangé wrote: >>>>> We have usually followed a rule that new machine types must not >>>>> affect runability of a VM on a host. IOW new machine types should >>>>> not introduce dependancies on specific kernels, or hardware features >>>>> such as CPU flags. >>>> >>>>> Anything that requires a new kernel feature thus ought to be an >>>>> opt-in config tunable on the CLI, separate from machine type >>>>> choice. >>>> >>>> Unless someone tinkered with the module parameters, they could not even >>>> use nested virtualization before 4.20. So for everyone else, "-cpu >>>> ...,+vmx" does count as an "opt-in config tunable on the CLI" that >>>> requires 4.20. >>>> >>>> For those that did tinker with module parameters, we can grandfather in >>>> the old machine types, so that they can use nested virtualization with >>>> no live migration support. For those that did not, however, I don't >>>> think it makes sense to say "oh by the way I really want to be able to >>>> migrate this VM" on the command line, or even worse on the monitor. >>> >>> IIUC, 4.20 is only required from POV of migration state. Is it thus >>> possible to just register a migration blocker if QEMU is launched >>> on a host with kernel < 4.20. >>> >>> Migration has always been busted historically, so those people using >>> nested VMX already won't be hurt by not having ability to live migrate >>> their VM, but could otherwise continue using them without being forced >>> to upgrade their kernel to fix a feature they're not even using. >> >> Yes, although I am a bit worried we might have a population of users >> that: >> a) Have enabled nesting >> b) Run VMs with vmx enabled > > >> c) Don't normally actually run nested guests >> d) Currently happily migrate. > > True, and (b) would include anyone using libvirt's host-model CPU. So if > you enabled nesting, have host-model for all guests, but only use nesting > in one of the guests, you'd be doomed. > > Is it possible for QEMU to determine if there are nested guests running or > not and conditionally block migration appropriately to ensure safety ? Only if kernel supports KVM_CAP_NESTED_STATE. See my reply to Dave in this thread. -Liran > > > Regards, > Daniel > -- > |: https://urldefense.proofpoint.com/v2/url?u=https-3A__berrange.com&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=DIzWfmRGWO1b6hzL9NRbIt41fiFcnPt0MC8917u4Qv0&e= -o- https://urldefense.proofpoint.com/v2/url?u=https-3A__www.flickr.com_photos_dberrange&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=CjA-joyt2Y9t5B4YzIiupfY8EEO58m4vbmnd45adzFI&e= :| > |: https://urldefense.proofpoint.com/v2/url?u=https-3A__libvirt.org&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=tD05tikOHMJhh_EeZ2Esoxb0oku3MPFmj-S2YHdUGm0&e= -o- https://urldefense.proofpoint.com/v2/url?u=https-3A__fstop138.berrange.com&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=YAh1WAoXQKEB6hkMmG6ZnJQETOFnq6eqQLmJokME80A&e= :| > |: https://urldefense.proofpoint.com/v2/url?u=https-3A__entangle-2Dphoto.org&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=90Mm1Qb-SHe8P63xwGp6gzMU1I5DEW6YX0ttG6TL_7g&e= -o- https://urldefense.proofpoint.com/v2/url?u=https-3A__www.instagram.com_dberrange&d=DwIDaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=eMOrT-7t7-tfRtTw2da9c1YTU0_tOFfkVIhj9mWv-Pc&s=l4NrrDdRzPClvYQdxQdfIW0geHPWcukeyOGX8QapwYA&e= :|
next prev parent reply other threads:[~2018-11-13 0:00 UTC|newest] Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-09-16 12:46 [QEMU PATCH v2 0/2]: KVM: i386: Add support for save and restore nested state Liran Alon 2018-09-16 12:46 ` [Qemu-devel] " Liran Alon 2018-09-16 12:46 ` [QEMU PATCH v2 1/2] i386: Compile CPUX86State xsave_buf only when support KVM or HVF Liran Alon 2018-09-16 12:46 ` [Qemu-devel] " Liran Alon 2018-09-16 12:46 ` [QEMU PATCH v2 2/2] KVM: i386: Add support for save and restore nested state Liran Alon 2018-09-16 12:46 ` [Qemu-devel] " Liran Alon 2018-10-08 17:21 ` [QEMU PATCH v2 0/2]: " Liran Alon 2018-10-08 17:21 ` [Qemu-devel] " Liran Alon 2018-10-15 18:10 ` Liran Alon 2018-10-15 18:10 ` [Qemu-devel] " Liran Alon 2018-10-31 1:03 ` Liran Alon 2018-10-31 1:03 ` [Qemu-devel] " Liran Alon 2018-10-31 18:17 ` Eduardo Habkost 2018-10-31 18:17 ` [Qemu-devel] " Eduardo Habkost 2018-10-31 18:19 ` Paolo Bonzini 2018-10-31 18:19 ` [Qemu-devel] " Paolo Bonzini 2018-10-31 18:50 ` Liran Alon 2018-10-31 18:50 ` [Qemu-devel] " Liran Alon 2018-10-31 18:59 ` Dr. David Alan Gilbert 2018-10-31 18:59 ` [Qemu-devel] " Dr. David Alan Gilbert 2018-10-31 23:17 ` Liran Alon 2018-10-31 23:17 ` [Qemu-devel] " Liran Alon 2018-11-01 13:10 ` Dr. David Alan Gilbert 2018-11-01 13:10 ` [Qemu-devel] " Dr. David Alan Gilbert 2018-11-01 15:23 ` Liran Alon 2018-11-01 15:23 ` [Qemu-devel] " Liran Alon 2018-11-01 15:56 ` Dr. David Alan Gilbert 2018-11-01 15:56 ` [Qemu-devel] " Dr. David Alan Gilbert 2018-11-01 16:45 ` Jim Mattson via Qemu-devel 2018-11-01 16:45 ` [Qemu-devel] " Jim Mattson 2018-11-02 3:46 ` Liran Alon 2018-11-02 3:46 ` [Qemu-devel] " Liran Alon 2018-11-02 9:40 ` Paolo Bonzini 2018-11-02 9:40 ` [Qemu-devel] " Paolo Bonzini 2018-11-02 12:35 ` Dr. David Alan Gilbert 2018-11-02 12:35 ` [Qemu-devel] " Dr. David Alan Gilbert 2018-11-02 12:40 ` Daniel P. Berrangé 2018-11-02 12:40 ` [Qemu-devel] " Daniel P. Berrangé 2018-11-04 22:12 ` Paolo Bonzini 2018-11-04 22:12 ` [Qemu-devel] " Paolo Bonzini 2018-11-02 12:59 ` Liran Alon 2018-11-02 12:59 ` [Qemu-devel] " Liran Alon 2018-11-02 16:44 ` Jim Mattson via Qemu-devel 2018-11-02 16:44 ` [Qemu-devel] " Jim Mattson 2018-11-02 16:58 ` Daniel P. Berrangé 2018-11-02 16:58 ` [Qemu-devel] " Daniel P. Berrangé 2018-11-02 17:01 ` Jim Mattson via Qemu-devel 2018-11-02 17:01 ` [Qemu-devel] " Jim Mattson 2018-11-02 16:54 ` Daniel P. Berrangé 2018-11-02 16:54 ` [Qemu-devel] " Daniel P. Berrangé 2018-11-02 16:58 ` Dr. David Alan Gilbert 2018-11-02 16:58 ` [Qemu-devel] " Dr. David Alan Gilbert 2018-11-04 22:19 ` Paolo Bonzini 2018-11-04 22:19 ` [Qemu-devel] " Paolo Bonzini 2018-11-12 16:18 ` Daniel P. Berrangé 2018-11-12 16:18 ` [Qemu-devel] " Daniel P. Berrangé 2018-11-12 16:50 ` Dr. David Alan Gilbert 2018-11-12 16:50 ` [Qemu-devel] " Dr. David Alan Gilbert 2018-11-12 16:53 ` Paolo Bonzini 2018-11-12 16:53 ` [Qemu-devel] " Paolo Bonzini 2018-11-12 16:54 ` Daniel P. Berrangé 2018-11-12 16:54 ` [Qemu-devel] " Daniel P. Berrangé 2018-11-13 0:00 ` Liran Alon [this message] 2018-11-13 0:00 ` Liran Alon 2018-11-13 0:07 ` Jim Mattson via Qemu-devel 2018-11-13 0:07 ` [Qemu-devel] " Jim Mattson 2018-11-13 0:09 ` Liran Alon 2018-11-13 0:09 ` [Qemu-devel] " Liran Alon 2018-11-12 23:58 ` Liran Alon 2018-11-12 23:58 ` [Qemu-devel] " Liran Alon 2018-11-02 16:39 ` Jim Mattson via Qemu-devel 2018-11-02 16:39 ` [Qemu-devel] " Jim Mattson 2018-11-03 2:02 ` Liran Alon 2018-11-03 2:02 ` [Qemu-devel] " Liran Alon 2018-11-08 0:13 ` Liran Alon 2018-11-08 0:13 ` [Qemu-devel] " Liran Alon 2018-11-08 0:45 ` Jim Mattson via Qemu-devel 2018-11-08 0:45 ` [Qemu-devel] " Jim Mattson 2018-11-08 9:50 ` Paolo Bonzini 2018-11-08 9:50 ` [Qemu-devel] " Paolo Bonzini 2018-11-08 9:57 ` Liran Alon 2018-11-08 9:57 ` [Qemu-devel] " Liran Alon 2018-11-08 17:02 ` Paolo Bonzini 2018-11-08 17:02 ` [Qemu-devel] " Paolo Bonzini 2018-11-08 18:41 ` Liran Alon 2018-11-08 18:41 ` [Qemu-devel] " Liran Alon 2018-11-08 20:34 ` Paolo Bonzini 2018-11-08 20:34 ` [Qemu-devel] " Paolo Bonzini 2018-11-12 14:51 ` Dr. David Alan Gilbert 2018-11-12 14:51 ` [Qemu-devel] " Dr. David Alan Gilbert 2018-11-01 19:03 ` Liran Alon 2018-11-01 19:03 ` [Qemu-devel] " Liran Alon 2018-11-01 19:07 ` Dr. David Alan Gilbert 2018-11-01 19:07 ` [Qemu-devel] " Dr. David Alan Gilbert 2018-11-01 19:41 ` Jim Mattson via Qemu-devel 2018-11-01 19:41 ` [Qemu-devel] " Jim Mattson
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