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kvm: x86: emulate monitor and mwait instructions as nop

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Treat monitor and mwait instructions as nop, which is architecturally
correct (but inefficient) behavior. We do this to prevent misbehaving
guests (e.g. OS X <= 10.7) from crashing after they fail to check for
monitor/mwait availability via cpuid.

Since mwait-based idle loops relying on these nop-emulated instructions
would keep the host CPU pegged at 100%, do NOT advertise their presence
via cpuid, to prevent compliant guests from using them inadvertently.

Signed-off-by: Gabriel L. Somlo <somlo@cmu.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Gabriel L. Somlo 2014-05-07 16:52:13 -04:00 • committed by Paolo Bonzini
parent b63cf42fd1
commit 87c00572ba
3 changed files with 38 additions and 12 deletions
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2
arch/x86/kvm/cpuid.c
View file

@ -283,6 +283,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
0 /* Reserved */ | f_lm | F(3DNOWEXT) | F(3DNOW); 0 /* Reserved */ | f_lm | F(3DNOWEXT) | F(3DNOW);
/* cpuid 1.ecx */ /* cpuid 1.ecx */
const u32 kvm_supported_word4_x86_features = const u32 kvm_supported_word4_x86_features =
/* NOTE: MONITOR (and MWAIT) are emulated as NOP,
* but *not* advertised to guests via CPUID ! */
F(XMM3) | F(PCLMULQDQ) | 0 /* DTES64, MONITOR */ | F(XMM3) | F(PCLMULQDQ) | 0 /* DTES64, MONITOR */ |
0 /* DS-CPL, VMX, SMX, EST */ | 0 /* DS-CPL, VMX, SMX, EST */ |
0 /* TM2 */ | F(SSSE3) | 0 /* CNXT-ID */ | 0 /* Reserved */ | 0 /* TM2 */ | F(SSSE3) | 0 /* CNXT-ID */ | 0 /* Reserved */ |

28
arch/x86/kvm/svm.c
View file

@ -2770,12 +2770,6 @@ static int xsetbv_interception(struct vcpu_svm *svm)
return 1; return 1;
} }
static int invalid_op_interception(struct vcpu_svm *svm)
{
kvm_queue_exception(&svm->vcpu, UD_VECTOR);
return 1;
}
static int task_switch_interception(struct vcpu_svm *svm) static int task_switch_interception(struct vcpu_svm *svm)
{ {
u16 tss_selector; u16 tss_selector;
@ -3287,6 +3281,24 @@ static int pause_interception(struct vcpu_svm *svm)
return 1; return 1;
} }
static int nop_interception(struct vcpu_svm *svm)
{
skip_emulated_instruction(&(svm->vcpu));
return 1;
}
static int monitor_interception(struct vcpu_svm *svm)
{
printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
return nop_interception(svm);
}
static int mwait_interception(struct vcpu_svm *svm)
{
printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
return nop_interception(svm);
}
static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = { static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
[SVM_EXIT_READ_CR0] = cr_interception, [SVM_EXIT_READ_CR0] = cr_interception,
[SVM_EXIT_READ_CR3] = cr_interception, [SVM_EXIT_READ_CR3] = cr_interception,
@ -3344,8 +3356,8 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
[SVM_EXIT_CLGI] = clgi_interception, [SVM_EXIT_CLGI] = clgi_interception,
[SVM_EXIT_SKINIT] = skinit_interception, [SVM_EXIT_SKINIT] = skinit_interception,
[SVM_EXIT_WBINVD] = emulate_on_interception, [SVM_EXIT_WBINVD] = emulate_on_interception,
[SVM_EXIT_MONITOR] = invalid_op_interception, [SVM_EXIT_MONITOR] = monitor_interception,
[SVM_EXIT_MWAIT] = invalid_op_interception, [SVM_EXIT_MWAIT] = mwait_interception,
[SVM_EXIT_XSETBV] = xsetbv_interception, [SVM_EXIT_XSETBV] = xsetbv_interception,
[SVM_EXIT_NPF] = pf_interception, [SVM_EXIT_NPF] = pf_interception,
}; };

20
arch/x86/kvm/vmx.c
View file

@ -5650,12 +5650,24 @@ static int handle_pause(struct kvm_vcpu *vcpu)
return 1; return 1;
} }
static int handle_invalid_op(struct kvm_vcpu *vcpu) static int handle_nop(struct kvm_vcpu *vcpu)
{ {
kvm_queue_exception(vcpu, UD_VECTOR); skip_emulated_instruction(vcpu);
return 1; return 1;
} }
static int handle_mwait(struct kvm_vcpu *vcpu)
{
printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
return handle_nop(vcpu);
}
static int handle_monitor(struct kvm_vcpu *vcpu)
{
printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
return handle_nop(vcpu);
}
/* /*
* To run an L2 guest, we need a vmcs02 based on the L1-specified vmcs12. * To run an L2 guest, we need a vmcs02 based on the L1-specified vmcs12.
* We could reuse a single VMCS for all the L2 guests, but we also want the * We could reuse a single VMCS for all the L2 guests, but we also want the
@ -6617,8 +6629,8 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[EXIT_REASON_EPT_VIOLATION] = handle_ept_violation, [EXIT_REASON_EPT_VIOLATION] = handle_ept_violation,
[EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig, [EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
[EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause, [EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
[EXIT_REASON_MWAIT_INSTRUCTION] = handle_invalid_op, [EXIT_REASON_MWAIT_INSTRUCTION] = handle_mwait,
[EXIT_REASON_MONITOR_INSTRUCTION] = handle_invalid_op, [EXIT_REASON_MONITOR_INSTRUCTION] = handle_monitor,
[EXIT_REASON_INVEPT] = handle_invept, [EXIT_REASON_INVEPT] = handle_invept,
}; };