KVM: VMX: Pass cr0.mp through to the guest when the fpu is active

When cr0.mp is clear, the guest doesn't expect a #NM in response to
a WAIT instruction.  Because we always keep cr0.mp set, it will get
a #NM, and potentially be confused.

Fix by keeping cr0.mp set only when the fpu is inactive, and passing
it through when inactive.

Reported-by: Lorenzo Martignoni <martignlo@gmail.com>
Analyzed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a680d939546f..7a56879a058c 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -66,7 +66,7 @@ module_param(emulate_invalid_guest_state, bool, S_IRUGO);
 #define KVM_GUEST_CR0_MASK                                              \
         (KVM_GUEST_CR0_MASK_UNRESTRICTED_GUEST | X86_CR0_PG | X86_CR0_PE)
 #define KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST                         \
-        (X86_CR0_WP | X86_CR0_NE | X86_CR0_MP)
+        (X86_CR0_WP | X86_CR0_NE)
 #define KVM_VM_CR0_ALWAYS_ON                                            \
         (KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST | X86_CR0_PG | X86_CR0_PE)
 #define KVM_CR4_GUEST_OWNED_BITS                                      \
@@ -791,12 +791,15 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
 
 static void vmx_fpu_activate(struct kvm_vcpu *vcpu)
 {
+        ulong cr0;
+
         if (vcpu->fpu_active)
                 return;
         vcpu->fpu_active = 1;
-        vmcs_clear_bits(GUEST_CR0, X86_CR0_TS);
-        if (kvm_read_cr0_bits(vcpu, X86_CR0_TS))
-                vmcs_set_bits(GUEST_CR0, X86_CR0_TS);
+        cr0 = vmcs_readl(GUEST_CR0);
+        cr0 &= ~(X86_CR0_TS | X86_CR0_MP);
+        cr0 |= kvm_read_cr0_bits(vcpu, X86_CR0_TS | X86_CR0_MP);
+        vmcs_writel(GUEST_CR0, cr0);
         update_exception_bitmap(vcpu);
         vcpu->arch.cr0_guest_owned_bits = X86_CR0_TS;
         vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
@@ -807,7 +810,7 @@ static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
 static void vmx_fpu_deactivate(struct kvm_vcpu *vcpu)
 {
         vmx_decache_cr0_guest_bits(vcpu);
-        vmcs_set_bits(GUEST_CR0, X86_CR0_TS);
+        vmcs_set_bits(GUEST_CR0, X86_CR0_TS | X86_CR0_MP);
         update_exception_bitmap(vcpu);
         vcpu->arch.cr0_guest_owned_bits = 0;
         vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
@@ -1757,7 +1760,7 @@ static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
                 ept_update_paging_mode_cr0(&hw_cr0, cr0, vcpu);
 
         if (!vcpu->fpu_active)
-                hw_cr0 |= X86_CR0_TS;
+                hw_cr0 |= X86_CR0_TS | X86_CR0_MP;
 
         vmcs_writel(CR0_READ_SHADOW, cr0);
         vmcs_writel(GUEST_CR0, hw_cr0);