Re: [Xen-devel] [PATCH] x86/traps: hypervisor leaf 0x40000010 timing info

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.09.14 at 06:11, <eshelton@xxxxxxxxx> wrote:
> In October 2008 (see http://http://lwn.net/Articles/301888/),
> VMware proposed (and now implements) a generic hypervisor leaf
> 0x40000010 to provide timing information - specifically, the TSC
> frequency and the bus frequency in kHz.  Some operating systems,
> including OS X, make use of these values to perform hypervisor-aware
> timing.  OS X makes use of this information without regard to the
> hypervisor vendor ID signature returned in leaf 0x40000000.

So that proposal talks (bogusly) about an these leaves being an
interface between hypervisors and _Linux_ guests, yet you claim
it's needed/desired for OS X. Apart from this just being a proposal
(with no indication towards where a proper specification would be),
making CPUID behavior depend on guest type is pretty contrary to
the general idea of full virtualization (where the hypervisor should
make as little assumptions about the guest as possible).

Also, btw., providing a proper link would have helped too.

As to the patch itself - is this

> +    case 5 ... 15:
> +        *eax = 0;          /* Reserved */
> +        *ebx = 0;          /* Reserved */
> +        *ecx = 0;          /* Reserved */
> +        *edx = 0;          /* Reserved */
> +        break;

really needed?

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel