On 12/22/20 11:41 AM, Sean Christopherson wrote: > On Tue, Dec 22, 2020, Babu Moger wrote: >> >> On 12/9/20 5:11 PM, Jim Mattson wrote: >>> On Wed, Dec 9, 2020 at 2:39 PM Babu Moger <babu.moger@xxxxxxx> wrote: >>>> >>>> On 12/7/20 5:22 PM, Jim Mattson wrote: >>>>> On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@xxxxxxx> wrote: >>>>>> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h >>>>>> index dad350d42ecf..d649ac5ed7c7 100644 >>>>>> --- a/arch/x86/include/asm/cpufeatures.h >>>>>> +++ b/arch/x86/include/asm/cpufeatures.h >>>>>> @@ -335,6 +335,7 @@ >>>>>> #define X86_FEATURE_AVIC (15*32+13) /* Virtual Interrupt Controller */ >>>>>> #define X86_FEATURE_V_VMSAVE_VMLOAD (15*32+15) /* Virtual VMSAVE VMLOAD */ >>>>>> #define X86_FEATURE_VGIF (15*32+16) /* Virtual GIF */ >>>>>> +#define X86_FEATURE_V_SPEC_CTRL (15*32+20) /* Virtual SPEC_CTRL */ >>>>> >>>>> Shouldn't this bit be reported by KVM_GET_SUPPORTED_CPUID when it's >>>>> enumerated on the host? >>>> >>>> Jim, I am not sure if this needs to be reported by >>>> KVM_GET_SUPPORTED_CPUID. I dont see V_VMSAVE_VMLOAD or VGIF being reported >>>> via KVM_GET_SUPPORTED_CPUID. Do you see the need for that? >>> >>> Every little bit helps. No, it isn't *needed*. But then again, this >>> entire patchset isn't *needed*, is it? >>> >> >> Working on v2 of these patches. Saw this code comment(in >> arch/x86/kvm/cpuid.c) on about exposing SVM features to the guest. >> >> >> /* >> * Hide all SVM features by default, SVM will set the cap bits for >> * features it emulates and/or exposes for L1. >> */ >> kvm_cpu_cap_mask(CPUID_8000_000A_EDX, 0); >> >> >> Should we go ahead with the changes here? > > Probably not, as the current SVM implementation aligns with the intended use of > KVM_GET_SUPPORTED_CPUID. The current approach is to enumerate what SVM features > KVM can virtualize or emulate for a nested VM, i.e. what SVM features an L1 VMM > can use and thus can be set in a vCPU's CPUID model. For V_SPEC_CTRL, I'm > pretty sure Jim was providing feedback for the non-nested case of reporting > host/KVM support of the feature itself. > > There is the question of whether or not KVM should have an ioctl() to report > what virtualization features are supported/enabled. AFAIK, it's not truly > required as userspace can glean the information via /proc/cpuinfo (especially > now that vmx_features exists), raw CPUID, and KVM module params. Providing an > ioctl() would likely be a bit cleaner for userspace, but I'm guessing that ship > has already sailed for most VMMs. > Sean, Thanks for the clarifications.
