Jeremy Fitzhardinge wrote: > Nakajima, Jun wrote: > > > Again, 0x40000000 is not Xen specific. If the leaf 0x40000000 is used > > for any guest to detect any hypervisor, that would be compelling > > benefit. For future Xen-specific features, it's safe for Xen to use > > other bigger leaves (like 0x40001000) because the guest starts looking > > at them after detection of Xen. > > > > Likewise if KVM paravirtualization interface (as kind of "open source > > paravirtualization interface") is detected in the generic areas (not in > > vender-specific), any guest can check the features available without > > knowing which hypervisor uses which CPUID for that. > > > > This just seems a bit grotty. You're relying on the fact that you can > overlay Xen's current use of 0x4000000x for the generic interface by > freezing Xen's current use of 40000000-2. 0x40000000 becomes a more or > less useless hypervisor-identification signature (useless because you > need to assume that leaves 4000000x, x>2 implement the generic interface > anyway, where x=1,2 are reserved for Xen (=hypervisor-specific) uses).
No, really. Xen just _implemented_ the generic interface from the beginning, at least for 0 and 1 (version). The 0x40000002 (hypercall page) looks specific to Xen, but it can be used for KVM as well, thus can be generic (or a hypervisor can tell it's not supported by returning 0 pages for hypercall pages). If Xen implements the new generic feature (defined by 0x40000003, for example), then it returns 40000003 or large for the max leaf upon CPUID.0x40000000. > > In other words, what mechanism can a guest use to explicitly identify > the existence of the generic interface? There needs to be a signature > for that somewhere. > > J So you don't need a signature for that. As I wrote before: 1. detect Xen or KVM <the list> using CPUID.0x40000000 2. Check the version if necessary using CPUID.0x40000001 3. Check the generic features available using CPUID.0x4000000Y, if the max leaf returned >= 0x4000000Y. A guest wants to want to know who the hypervior is for practical purposes (e.g. debuggging) anyway. This is equivalent to what a native OS would do to detect a generic CPU feature. Jun --- Intel Open Source Technology Center - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
