[PATCH] KVM: VMX: Fix clts

[PATCH] KVM: VMX: Fix clts

[Avi Kivity]

The simplistic clts implementation has a couple of flaws:
- kvm_read_cr0_bits() is temporarily unsynchronized when vcpu->arch.cr0 changes
- if the fpu is active, we need to clear GUEST_CR0.TS, not just
  CR_READ_SHADOW.TS, so that we don't send the guest an unexpected #NM.

Fix by replacing custom logic with a call to vmx_set_cr0(), which does the
right thing, albeit less efficiently.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 arch/x86/kvm/vmx.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9f56110..d27ff6a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3007,8 +3007,7 @@ static int handle_cr(struct kvm_vcpu *vcpu)
 		};
 		break;
 	case 2: /* clts */
-		vcpu->arch.cr0 &= ~X86_CR0_TS;
-		vmcs_writel(CR0_READ_SHADOW, kvm_read_cr0(vcpu));
+		vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
 		trace_kvm_cr_write(0, kvm_read_cr0(vcpu));
 		skip_emulated_instruction(vcpu);
 		return 1;
-- 
1.6.5.3

Re: [PATCH] KVM: VMX: Fix clts

[Marcelo Tosatti]

On Sun, Jan 24, 2010 at 12:17:23PM +0200, Avi Kivity wrote:
> The simplistic clts implementation has a couple of flaws:
> - kvm_read_cr0_bits() is temporarily unsynchronized when vcpu->arch.cr0 changes
> - if the fpu is active, we need to clear GUEST_CR0.TS, not just
>   CR_READ_SHADOW.TS, so that we don't send the guest an unexpected #NM.
> 
> Fix by replacing custom logic with a call to vmx_set_cr0(), which does the
> right thing, albeit less efficiently.
> 
> Signed-off-by: Avi Kivity <avi@redhat.com>

Applied, thanks.