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KVM paravirtualization on non-VMX/SVM CPUs?

DISCUSSION Tomasz Chmielewski 3 participants 3 messages Mar 19, 2007 1 message not in the archive KVM

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In January, Ingo Molnar announced "KVM paravirtualization for Linux"[1].

The announcement mentions "support for the hardware cr3-cache feature of Intel-VMX CPUs" and "i only tested this on 32-bit VMX".

Because of this, I'm not sure how to understand it:

1) KVM paravirtualization means that it will be possible to use KVM on non-VMX/SVM CPUs (much like Xen)?

2) KVM paravirtualization means paravirtualized drivers only (net, disk etc.), but it will still run only on VMX/SVM-capable CPUs?

Which one is true? First, or second?

[1] http://people.redhat.com/mingo/kvm-paravirt-patches/ANNOUNCE

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Tomasz Chmielewski
http://wpkg.org

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#2 lore raw
Quoted 7 lines · Tomasz Chmielewski

In January, Ingo Molnar announced "KVM paravirtualization for Linux"[1].

The announcement mentions "support for the hardware cr3-cache feature of Intel-VMX CPUs" and "i only tested this on 32-bit VMX".

Because of this, I'm not sure how to understand it:

Quoted 8 lines

1) KVM paravirtualization means that it will be possible to use KVM on non-VMX/SVM CPUs (much like Xen)?

2) KVM paravirtualization means paravirtualized drivers only (net, disk etc.), but it will still run only on VMX/SVM-capable CPUs?

Which one is true? First, or second?

The latter. I asked this question several weeks ago. The response
was that it "would be nice" for KVM to support non-VMX machines, but that it wasn't a priority in any way for any of the current developers.

My understanding is that the paravirtualisation support that Ingo
wrote is purely for performance purposes, bypassing the hardware emulation layer in qemu and going directly to the host VM's device layer.

Hugo.

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Quoted 10 lines · Tomasz Chmielewski

In January, Ingo Molnar announced "KVM paravirtualization for Linux"[1].

The announcement mentions "support for the hardware cr3-cache feature of Intel-VMX CPUs" and "i only tested this on 32-bit VMX".

Because of this, I'm not sure how to understand it:

1) KVM paravirtualization means that it will be possible to use KVM on non-VMX/SVM CPUs (much like Xen)?

No. That is possible (and kqemu demonstrates it can be done), but it is not implemented and to my knowledge no one is working on it.

Quoted 5 lines

2) KVM paravirtualization means paravirtualized drivers only (net, disk etc.), but it will still run only on VMX/SVM-capable CPUs?

Yes. In addition, it enables platform-level optimization (like the cr3 cache).

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