From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754357AbYI0AOd (ORCPT ); Fri, 26 Sep 2008 20:14:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752687AbYI0AOX (ORCPT ); Fri, 26 Sep 2008 20:14:23 -0400 Received: from terminus.zytor.com ([198.137.202.10]:60909 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752000AbYI0AOW (ORCPT ); Fri, 26 Sep 2008 20:14:22 -0400 Message-ID: <48DD799C.3070706@zytor.com> Date: Fri, 26 Sep 2008 17:09:00 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: akataria@vmware.com CC: Ingo Molnar , Thomas Gleixner , LKML , the arch/x86 maintainers , Jeremy Fitzhardinge , avi@redhat.com, Rusty Russell , Zachary Amsden , Dan Hecht , Jun.Nakajima@Intel.Com Subject: Re: Use CPUID to communicate with the hypervisor. References: <1222472815.29886.43.camel@alok-dev1> In-Reply-To: <1222472815.29886.43.camel@alok-dev1> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alok Kataria wrote: > From: Alok N Kataria > > This patch proposes to use a cpuid interface to detect if we are running on an > hypervisor. > The discovery of a hypervisor is determined by bit 31 of CPUID#1_ECX, which is > defined to be "hypervisor present bit". For a VM, the bit is 1, otherwise it is > set to 0. This bit is not officially documented by either Intel/AMD yet, but > they plan to do so some time soon, in the meanwhile they have promised to keep > it reserved for virtualization. > > Also, 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. > XEN/KVM are already using the info leaf to get the hypervisor signature. > > VMware hardware version 7 defines some of these cpuid levels, below is a brief > description about those. These levels can be implemented by other hypervisors > too so that Linux has a standard way of communicating to any hypervisor. > > 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). > > +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. > --- 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. 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. > 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 > + 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 , but otherwise wouldn't be entirely wrong. -hpa