| Message ID | 1489448438-29865-1-git-send-email-mst@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
2017-03-14 01:44+0200, Michael S. Tsirkin: > Guests running Mac OS 5, 6, and 7 (Leopard through Lion) have a problem: > unless explicitly provided with kernel command line argument > "idlehalt=0" they'd implicitly assume MONITOR and MWAIT availability, > without checking CPUID. > > We currently emulate that as a NOP but on VMX we can do better: let > guest stop the CPU until timer, IPI or memory change. CPU will be busy > but that isn't any worse than a NOP emulation. > > Note that mwait within guests is not the same as on real hardware > because halt causes an exit while mwait doesn't. For this reason it > might not be a good idea to use the regular MWAIT flag in CPUID to > signal this capability. Add a flag in the hypervisor leaf instead. > > Additionally, we add a capability for QEMU - e.g. if it knows there's an > isolated CPU dedicated for the VCPU it can set the standard MWAIT flag > to improve guest behaviour. > > Reported-by: "Gabriel L. Somlo" <gsomlo@gmail.com> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > --- > > Note: SVM bits are untested at this point. Seems pretty > obvious though. > > changes from v2: > - add a capability to allow host userspace to detect new kernels > - more documentation to clarify the semantics of the feature flag > and why it's useful > - svm support as suggested by Radim > > changes from v1: > - typo fix resulting in rest of leaf flags being overwritten > Reported by: Wanpeng Li <kernellwp@gmail.com> > - updated commit log with data about guests helped by this feature > - better document differences between mwait and halt for guests > > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt > @@ -4135,11 +4135,11 @@ available, means that that the kernel can support guests using the > radix MMU defined in Power ISA V3.00 (as implemented in the POWER9 > processor). > > -8.4 KVM_CAP_PPC_HASH_MMU_V3 This patch should not not remove the PPC capability from docs. (The right name is KVM_CAP_PPC_HASH_V3, but that is for another patch.) > +8.5 KVM_CAP_X86_GUEST_MWAIT > > -Architectures: ppc > +Architectures: x86 > > -This capability, if KVM_CHECK_EXTENSION indicates that it is > -available, means that that the kernel can support guests using the > -hashed page table MMU defined in Power ISA V3.00 (as implemented in > -the POWER9 processor), including in-memory segment tables. > +This capability indicates that guest using memory monotoring instructions > +(MWAIT/MWAITX) to stop the virtual CPU will not cause a VM exit. As such time > +spent while virtual CPU is halted in this way will then be accounted for as > +guest running time on the host (as opposed to e.g. HLT). > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > @@ -2684,6 +2684,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > case KVM_CAP_ADJUST_CLOCK: > r = KVM_CLOCK_TSC_STABLE; > break; > + case KVM_CAP_X86_GUEST_MWAIT: > + r = !!this_cpu_has(X86_FEATURE_MWAIT); this_cpu_has already returns bool, so !! is not needed. I can fix both while applying. > + break; > case KVM_CAP_X86_SMM: > /* SMBASE is usually relocated above 1M on modern chipsets, > * and SMM handlers might indeed rely on 4G segment limits,
On Tue, Mar 14, 2017 at 02:58:24PM +0100, Radim Krčmář wrote: > 2017-03-14 01:44+0200, Michael S. Tsirkin: > > Guests running Mac OS 5, 6, and 7 (Leopard through Lion) have a problem: > > unless explicitly provided with kernel command line argument > > "idlehalt=0" they'd implicitly assume MONITOR and MWAIT availability, > > without checking CPUID. > > > > We currently emulate that as a NOP but on VMX we can do better: let > > guest stop the CPU until timer, IPI or memory change. CPU will be busy > > but that isn't any worse than a NOP emulation. > > > > Note that mwait within guests is not the same as on real hardware > > because halt causes an exit while mwait doesn't. For this reason it > > might not be a good idea to use the regular MWAIT flag in CPUID to > > signal this capability. Add a flag in the hypervisor leaf instead. > > > > Additionally, we add a capability for QEMU - e.g. if it knows there's an > > isolated CPU dedicated for the VCPU it can set the standard MWAIT flag > > to improve guest behaviour. > > > > Reported-by: "Gabriel L. Somlo" <gsomlo@gmail.com> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > --- > > > > Note: SVM bits are untested at this point. Seems pretty > > obvious though. > > > > changes from v2: > > - add a capability to allow host userspace to detect new kernels > > - more documentation to clarify the semantics of the feature flag > > and why it's useful > > - svm support as suggested by Radim > > > > changes from v1: > > - typo fix resulting in rest of leaf flags being overwritten > > Reported by: Wanpeng Li <kernellwp@gmail.com> > > - updated commit log with data about guests helped by this feature > > - better document differences between mwait and halt for guests > > > > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt > > @@ -4135,11 +4135,11 @@ available, means that that the kernel can support guests using the > > radix MMU defined in Power ISA V3.00 (as implemented in the POWER9 > > processor). > > > > -8.4 KVM_CAP_PPC_HASH_MMU_V3 > > This patch should not not remove the PPC capability from docs. > > (The right name is KVM_CAP_PPC_HASH_V3, but that is for another patch.) Oops my bad. If you do decide you want me to respin because of this, pls let me know. > > +8.5 KVM_CAP_X86_GUEST_MWAIT > > > > -Architectures: ppc > > +Architectures: x86 > > > > -This capability, if KVM_CHECK_EXTENSION indicates that it is > > -available, means that that the kernel can support guests using the > > -hashed page table MMU defined in Power ISA V3.00 (as implemented in > > -the POWER9 processor), including in-memory segment tables. > > +This capability indicates that guest using memory monotoring instructions > > +(MWAIT/MWAITX) to stop the virtual CPU will not cause a VM exit. As such time > > +spent while virtual CPU is halted in this way will then be accounted for as > > +guest running time on the host (as opposed to e.g. HLT). > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > @@ -2684,6 +2684,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > > case KVM_CAP_ADJUST_CLOCK: > > r = KVM_CLOCK_TSC_STABLE; > > break; > > + case KVM_CAP_X86_GUEST_MWAIT: > > + r = !!this_cpu_has(X86_FEATURE_MWAIT); > > this_cpu_has already returns bool, so !! is not needed. > > I can fix both while applying. OK, pls let me know if you need any more. > > + break; > > case KVM_CAP_X86_SMM: > > /* SMBASE is usually relocated above 1M on modern chipsets, > > * and SMM handlers might indeed rely on 4G segment limits,
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index 0694509..c7beb07 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -4135,11 +4135,11 @@ available, means that that the kernel can support guests using the radix MMU defined in Power ISA V3.00 (as implemented in the POWER9 processor). -8.4 KVM_CAP_PPC_HASH_MMU_V3 +8.5 KVM_CAP_X86_GUEST_MWAIT -Architectures: ppc +Architectures: x86 -This capability, if KVM_CHECK_EXTENSION indicates that it is -available, means that that the kernel can support guests using the -hashed page table MMU defined in Power ISA V3.00 (as implemented in -the POWER9 processor), including in-memory segment tables. +This capability indicates that guest using memory monotoring instructions +(MWAIT/MWAITX) to stop the virtual CPU will not cause a VM exit. As such time +spent while virtual CPU is halted in this way will then be accounted for as +guest running time on the host (as opposed to e.g. HLT). diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index 3c65feb..04c201c 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -54,6 +54,12 @@ KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit || || before enabling paravirtualized || || spinlock support. ------------------------------------------------------------------------------ +KVM_FEATURE_MWAIT || 8 || guest can use monitor/mwait + || || to halt the VCPU without exits, + || || time spent while halted in this + || || way is accounted for on host as + || || VCPU run time. +------------------------------------------------------------------------------ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h index cff0bb6..9cc77a7 100644 --- a/arch/x86/include/uapi/asm/kvm_para.h +++ b/arch/x86/include/uapi/asm/kvm_para.h @@ -24,6 +24,7 @@ #define KVM_FEATURE_STEAL_TIME 5 #define KVM_FEATURE_PV_EOI 6 #define KVM_FEATURE_PV_UNHALT 7 +#define KVM_FEATURE_MWAIT 8 /* The last 8 bits are used to indicate how to interpret the flags field * in pvclock structure. If no bits are set, all flags are ignored. diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index efde6cc..3c7fca83 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -594,6 +594,9 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, if (sched_info_on()) entry->eax |= (1 << KVM_FEATURE_STEAL_TIME); + if (this_cpu_has(X86_FEATURE_MWAIT)) + entry->eax |= (1 << KVM_FEATURE_MWAIT); + entry->ebx = 0; entry->ecx = 0; entry->edx = 0; diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index d1efe2c..18e53bc 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1198,8 +1198,6 @@ static void init_vmcb(struct vcpu_svm *svm) set_intercept(svm, INTERCEPT_CLGI); set_intercept(svm, INTERCEPT_SKINIT); set_intercept(svm, INTERCEPT_WBINVD); - set_intercept(svm, INTERCEPT_MONITOR); - set_intercept(svm, INTERCEPT_MWAIT); set_intercept(svm, INTERCEPT_XSETBV); control->iopm_base_pa = iopm_base; diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 4bfe349..b167aba 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -3547,13 +3547,9 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf) CPU_BASED_USE_IO_BITMAPS | CPU_BASED_MOV_DR_EXITING | CPU_BASED_USE_TSC_OFFSETING | - CPU_BASED_MWAIT_EXITING | - CPU_BASED_MONITOR_EXITING | CPU_BASED_INVLPG_EXITING | CPU_BASED_RDPMC_EXITING; - printk(KERN_ERR "cleared CPU_BASED_MWAIT_EXITING + CPU_BASED_MONITOR_EXITING\n"); - opt = CPU_BASED_TPR_SHADOW | CPU_BASED_USE_MSR_BITMAPS | CPU_BASED_ACTIVATE_SECONDARY_CONTROLS; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1faf620..a507635 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2684,6 +2684,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_ADJUST_CLOCK: r = KVM_CLOCK_TSC_STABLE; break; + case KVM_CAP_X86_GUEST_MWAIT: + r = !!this_cpu_has(X86_FEATURE_MWAIT); + break; case KVM_CAP_X86_SMM: /* SMBASE is usually relocated above 1M on modern chipsets, * and SMM handlers might indeed rely on 4G segment limits, diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index f51d508..8b6bc06 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -883,6 +883,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_PPC_MMU_RADIX 134 #define KVM_CAP_PPC_MMU_HASH_V3 135 #define KVM_CAP_IMMEDIATE_EXIT 136 +#define KVM_CAP_X86_GUEST_MWAIT 137 #ifdef KVM_CAP_IRQ_ROUTING
Guests running Mac OS 5, 6, and 7 (Leopard through Lion) have a problem: unless explicitly provided with kernel command line argument "idlehalt=0" they'd implicitly assume MONITOR and MWAIT availability, without checking CPUID. We currently emulate that as a NOP but on VMX we can do better: let guest stop the CPU until timer, IPI or memory change. CPU will be busy but that isn't any worse than a NOP emulation. Note that mwait within guests is not the same as on real hardware because halt causes an exit while mwait doesn't. For this reason it might not be a good idea to use the regular MWAIT flag in CPUID to signal this capability. Add a flag in the hypervisor leaf instead. Additionally, we add a capability for QEMU - e.g. if it knows there's an isolated CPU dedicated for the VCPU it can set the standard MWAIT flag to improve guest behaviour. Reported-by: "Gabriel L. Somlo" <gsomlo@gmail.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- Note: SVM bits are untested at this point. Seems pretty obvious though. changes from v2: - add a capability to allow host userspace to detect new kernels - more documentation to clarify the semantics of the feature flag and why it's useful - svm support as suggested by Radim changes from v1: - typo fix resulting in rest of leaf flags being overwritten Reported by: Wanpeng Li <kernellwp@gmail.com> - updated commit log with data about guests helped by this feature - better document differences between mwait and halt for guests Documentation/virtual/kvm/api.txt | 12 ++++++------ Documentation/virtual/kvm/cpuid.txt | 6 ++++++ arch/x86/include/uapi/asm/kvm_para.h | 1 + arch/x86/kvm/cpuid.c | 3 +++ arch/x86/kvm/svm.c | 2 -- arch/x86/kvm/vmx.c | 4 ---- arch/x86/kvm/x86.c | 3 +++ include/uapi/linux/kvm.h | 1 + 8 files changed, 20 insertions(+), 12 deletions(-)