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authorKarimAllah Ahmed <karahmed@amazon.de>2018-04-10 14:15:46 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2018-04-10 17:19:44 +0200
commit386c6ddbda180676b7d9fc375d54a7bdd353d39e (patch)
tree6544b98c691fa8ce69940a6d03bebb3badaa120b /arch/x86
parente01bca2fc698d7f0626f0214001af523e18ad60b (diff)
X86/VMX: Disable VMX preemption timer if MWAIT is not intercepted
The VMX-preemption timer is used by KVM as a way to set deadlines for the guest (i.e. timer emulation). That was safe till very recently when capability KVM_X86_DISABLE_EXITS_MWAIT to disable intercepting MWAIT was introduced. According to Intel SDM 25.5.1: """ The VMX-preemption timer operates in the C-states C0, C1, and C2; it also operates in the shutdown and wait-for-SIPI states. If the timer counts down to zero in any state other than the wait-for SIPI state, the logical processor transitions to the C0 C-state and causes a VM exit; the timer does not cause a VM exit if it counts down to zero in the wait-for-SIPI state. The timer is not decremented in C-states deeper than C2. """ Now once the guest issues the MWAIT with a c-state deeper than C2 the preemption timer will never wake it up again since it stopped ticking! Usually this is compensated by other activities in the system that would wake the core from the deep C-state (and cause a VMExit). For example, if the host itself is ticking or it received interrupts, etc! So disable the VMX-preemption timer if MWAIT is exposed to the guest! Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: kvm@vger.kernel.org Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de> Fixes: 4d5422cea3b61f158d58924cbb43feada456ba5c Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kvm/vmx.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index ce639e00fd0f..e7024ad586f7 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -12218,10 +12218,16 @@ static inline int u64_shl_div_u64(u64 a, unsigned int shift,
static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc)
{
- struct vcpu_vmx *vmx = to_vmx(vcpu);
- u64 tscl = rdtsc();
- u64 guest_tscl = kvm_read_l1_tsc(vcpu, tscl);
- u64 delta_tsc = max(guest_deadline_tsc, guest_tscl) - guest_tscl;
+ struct vcpu_vmx *vmx;
+ u64 tscl, guest_tscl, delta_tsc;
+
+ if (kvm_mwait_in_guest(vcpu->kvm))
+ return -EOPNOTSUPP;
+
+ vmx = to_vmx(vcpu);
+ tscl = rdtsc();
+ guest_tscl = kvm_read_l1_tsc(vcpu, tscl);
+ delta_tsc = max(guest_deadline_tsc, guest_tscl) - guest_tscl;
/* Convert to host delta tsc if tsc scaling is enabled */
if (vcpu->arch.tsc_scaling_ratio != kvm_default_tsc_scaling_ratio &&