Messages in this thread |  | | | Subject | Re: Use CPUID to communicate with the hypervisor. | | From | Alok Kataria <> | | Date | Fri, 26 Sep 2008 17:30:03 -0700 |
| |
Hi Peter,
Thanks for the comments, please find my replies below.
On Fri, 2008-09-26 at 17:09 -0700, H. Peter Anvin wrote: > Alok Kataria wrote:
> > > > Leaf 0x40000000, Hypervisor CPUID information > > # EAX: The maximum input value for hypervisor CPUID info (0x40000010). > > # EBX, ECX, EDX: Hypervisor vendor ID signature. E.g. "VMwareVMware" > > > > This is great, obviously... although we'll have to deal with legacy > methods for a while if not indefinitely (just as we have to for > pre-CPUID processors).
Ok, do you think we should keep those (legacy) interfaces separate so that they can be phased out whenever the time is right.
> > > > > +static void __init detect_hypervisor(void) > > +{ > > + if (cpu_has_hypervisor) { > > + unsigned int eax, ebx, ecx, edx; > > + char hyper_vendor_id[13]; > > + > > + cpuid(HYPERVISOR_INFO_LEAF, &eax, &ebx, &ecx, &edx); > > + memcpy(hyper_vendor_id + 0, &ebx, 4); > > + memcpy(hyper_vendor_id + 4, &ecx, 4); > > + memcpy(hyper_vendor_id + 8, &edx, 4); > > + hyper_vendor_id[12] = '\0'; > > + printk(KERN_INFO "Hypervisor vendor id %s\n", hyper_vendor_id); > > + } > > +} > > + > > This should be broken out into a separate file in cpu/*, because we > *will* need to detect hypervisors by other means. Ok, i will do that.
> > --- a/arch/x86/kernel/tsc.c > > +++ b/arch/x86/kernel/tsc.c > > @@ -345,16 +345,38 @@ failed: > > return 0; > > } > > > > +unsigned long hypervisor_tsc_freq(void) > > +{ > > + unsigned long tsc_khz; > > + unsigned int max_cpuid_leaf; > > + > > + if (cpu_has_hypervisor) { > > + max_cpuid_leaf = cpuid_eax(HYPERVISOR_INFO_LEAF); > > + if (max_cpuid_leaf >= HYPERVISOR_TIMING_LEAF) { > > + tsc_khz = cpuid_eax(HYPERVISOR_TIMING_LEAF); > > + printk(KERN_INFO > > + "TSC frequency read from hypervisor\n"); > > + return tsc_khz; > > + } > > + } > > + return 0; > > +} > > + > > I would call this "vmware_tsc_freq()" because it is a VMWare-defined > interface... you can't just poke at 0x40000010 and assume it is using > the VMWare definition.
I would like to see this as a generic hypervisor way to get frequency rather than a VMware specific thingy. > > In order for *that* to be safe, you'd have to have well-defined ranges > for different virtualization vendors where each of them can define their > own stuff.
My motivation for doing this is to have a standard across all the hypervisor's. If all the different hypervisor guys can come to some sought of consensus on the various hypervisor leafs that would help keep this simple and a lot more maintainable.
> > > diff --git a/include/asm-x86/processor.h b/include/asm-x86/processor.h > > index ee7cbb3..70ca49b 100644 > > --- a/include/asm-x86/processor.h > > +++ b/include/asm-x86/processor.h > > @@ -124,6 +124,27 @@ struct cpuinfo_x86 { > > #define X86_VENDOR_UNKNOWN 0xff > > > > /* > > + * Intel & AMD have reserved the cpuid levels 0x40000000 - 0x400000FF for > > + * software use. Hypervisors can use these levels to provide an interface > > + * to pass information from the hypervisor to the guest. This is similar > > + * to how we extract information about a physical cpu by using cpuid. > > + */ > > + > > +/* > > + * This CPUID leaf returns the information about the hypervisor. > > + * EAX : maximum input value for CPUID supported by the hypervisor. > > + * EBX, ECX, EDX : Hypervisor vendor ID signature. E.g. VMwareVMware. > > + */ > > +#define HYPERVISOR_INFO_LEAF 0x40000000 > > +/* > > + * This leaf gets timing information from the hypervisor. > > + * EAX: (Virtual) TSC frequency in kHz. > > + * EBX: (Virtual) Bus (local apic timer) frequency in kHz. > > + * ECX, EDX: RESERVED > > + */ > > +#define HYPERVISOR_TIMING_LEAF 0x40000010 > > + > > <asm/processor.h> is the wrong place for this, and these constants > should have CPUID_ in them to tell what they fundamentally are. > > My preference would be for <asm/cpuid.h>, but otherwise > <asm/cpufeature.h> wouldn't be entirely wrong.
Ok makes sense, will do that.
Thanks, Alok > > -hpa
|  |