Messages in this thread | | | Date | Mon, 11 May 2009 21:02:29 +0300 | From | Avi Kivity <> | Subject | Re: [RFC PATCH 0/3] generic hypercall support |
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Anthony Liguori wrote: >> >> It's a question of cost vs. benefit. It's clear the benefit is low >> (but that doesn't mean it's not worth having). The cost initially >> appeared to be very low, until the nested virtualization wrench was >> thrown into the works. Not that nested virtualization is a reality >> -- even on svm where it is implemented it is not yet production >> quality and is disabled by default. >> >> Now nested virtualization is beginning to look interesting, with >> Windows 7's XP mode requiring virtualization extensions. Desktop >> virtualization is also something likely to use device assignment >> (though you probably won't assign a virtio device to the XP instance >> inside Windows 7). >> >> Maybe we should revisit the mmio hypercall idea again, it might be >> workable if we find a way to let the guest know if it should use the >> hypercall or not for a given memory range. >> >> mmio hypercall is nice because >> - it falls back nicely to pure mmio >> - it optimizes an existing slow path, not just new device models >> - it has preexisting semantics, so we have less ABI to screw up >> - for nested virtualization + device assignment, we can drop it and >> get a nice speed win (or rather, less speed loss) > > If it's a PCI device, then we can also have an interrupt which we > currently lack with vmcall-based hypercalls. This would give us > guestcalls, upcalls, or whatever we've previously decided to call them.
Sorry, I totally failed to understand this. Please explain.
-- Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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