Nakajima, Jun wrote:
Jeremy Fitzhardinge wrote:
Nakajima, Jun wrote:
The hypervisor detection machanism is generic, and the signature
returned is implentation specific. Having a list of all hypervisor
signatures sounds fine to me as we are detecting vendor-specific
processor(s) in the native. And I don't expect the list is large.
I'm confused about what you're proposing. I was thinking that a
kernel
looking for the generic hypervisor interface would check for a
specific
signature at some cpuid leaf, and then go about using it from there.
If
not, how does is it supposed to detect the generic hypervisor
interface?
J
I'm suggesting that we use CPUID.0x4000000Y (Y: TBD, e.g. 6) for Linux
paravirtualization. The ebx, ecx and edx return the Linux
paravirtualization features available on that hypervisor. Those features
are defined architecturally (not VMM specific).
Like CPUID.0, CPUID.0x40000000 is used to detect the hypervisor with the
vendor identification string returned in ebx, edx, and ecx (as we are
doing in Xen). The eax returns the max leaf (which is 0x40000002 on Xen
today).
I don't understand the purpose of returning the max leaf. Who is that
information useful for?
I like Jeremy's suggesting of starting with 0x40001000 for KVM. Xen has
an established hypercall interface and that isn't going to change.
However, in the future, if other Operating Systems (like the BSDs)
choose to implement the KVM paravirtualization interface, then that
leaves open the possibility for Xen to also support this interface to
get good performance for those OSes. It's necessary to be able to
support both at once if you wish to support these interfaces without
user interaction.
There's no tangible benefit to us to use 0x40000000. Therefore I'm
inclined to lean toward making things easier for others.
Regards,
Anthony Liguori
And like CPUID.1, CPUID.0x40000001 returns the version number in
eax, and each VMM should be able to define a number of VMM-specific
features available in ebx, ecx, and edx returned (which are reserved,
i.e. not used in Xen today).
Suppose we knew (i.e. tested) Xen and KVM supported Linux
paravirtualization, the Linux code does:
1. detect Xen or KVM <the list> using CPUID.0x40000000
2. Check the version if necessary using CPUID.0x40000001
3. Check the Linux paravirtualization features available using
CPUID.0x4000000Y.
Jun
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