| Message ID | 160738067105.28590.10158084163761735153.stgit@bmoger-ubuntu (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86: Add the feature Virtual SPEC_CTRL | expand |
On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@amd.com> wrote: > > Newer AMD processors have a feature to virtualize the use of the SPEC_CTRL > MSR. This feature is identified via CPUID 0x8000000A_EDX[20]. When present, > the SPEC_CTRL MSR is automatically virtualized and no longer requires > hypervisor intervention. > > Signed-off-by: Babu Moger <babu.moger@amd.com> > --- > arch/x86/include/asm/cpufeatures.h | 1 + > 1 file changed, 1 insertion(+) > > 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? > /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */ > #define X86_FEATURE_AVX512VBMI (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/ >
On 12/7/20 5:22 PM, Jim Mattson wrote: > On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@amd.com> wrote: >> >> Newer AMD processors have a feature to virtualize the use of the SPEC_CTRL >> MSR. This feature is identified via CPUID 0x8000000A_EDX[20]. When present, >> the SPEC_CTRL MSR is automatically virtualized and no longer requires >> hypervisor intervention. >> >> Signed-off-by: Babu Moger <babu.moger@amd.com> >> --- >> arch/x86/include/asm/cpufeatures.h | 1 + >> 1 file changed, 1 insertion(+) >> >> 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? >> /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */ >> #define X86_FEATURE_AVX512VBMI (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/ >>
On Wed, Dec 9, 2020 at 2:39 PM Babu Moger <babu.moger@amd.com> wrote: > > > > On 12/7/20 5:22 PM, Jim Mattson wrote: > > On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@amd.com> wrote: > >> > >> Newer AMD processors have a feature to virtualize the use of the SPEC_CTRL > >> MSR. This feature is identified via CPUID 0x8000000A_EDX[20]. When present, > >> the SPEC_CTRL MSR is automatically virtualized and no longer requires > >> hypervisor intervention. > >> > >> Signed-off-by: Babu Moger <babu.moger@amd.com> > >> --- > >> arch/x86/include/asm/cpufeatures.h | 1 + > >> 1 file changed, 1 insertion(+) > >> > >> 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?
On 12/9/20 5:11 PM, Jim Mattson wrote: > On Wed, Dec 9, 2020 at 2:39 PM Babu Moger <babu.moger@amd.com> wrote: >> >> >> >> On 12/7/20 5:22 PM, Jim Mattson wrote: >>> On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@amd.com> wrote: >>>> >>>> Newer AMD processors have a feature to virtualize the use of the SPEC_CTRL >>>> MSR. This feature is identified via CPUID 0x8000000A_EDX[20]. When present, >>>> the SPEC_CTRL MSR is automatically virtualized and no longer requires >>>> hypervisor intervention. >>>> >>>> Signed-off-by: Babu Moger <babu.moger@amd.com> >>>> --- >>>> arch/x86/include/asm/cpufeatures.h | 1 + >>>> 1 file changed, 1 insertion(+) >>>> >>>> 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? Thanks Babu
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@amd.com> wrote: > >> > >> On 12/7/20 5:22 PM, Jim Mattson wrote: > >>> On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@amd.com> 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.
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@amd.com> wrote: >>>> >>>> On 12/7/20 5:22 PM, Jim Mattson wrote: >>>>> On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@amd.com> 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.
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 */ /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */ #define X86_FEATURE_AVX512VBMI (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/
Newer AMD processors have a feature to virtualize the use of the SPEC_CTRL MSR. This feature is identified via CPUID 0x8000000A_EDX[20]. When present, the SPEC_CTRL MSR is automatically virtualized and no longer requires hypervisor intervention. Signed-off-by: Babu Moger <babu.moger@amd.com> --- arch/x86/include/asm/cpufeatures.h | 1 + 1 file changed, 1 insertion(+)