[PATCH] KVM: Prevent stale bits in cr0 and cr4

Hardware virtualization implementations allow the guests to freely change some
of the bits in cr0 and cr4, but trap when changing the other bits.  This is
useful to avoid excessive exits due to changing, for example, the ts flag.

It also means the kvm's copy of cr0 and cr4 may be stale with respect to these
bits.  most of the time this doesn't matter as these bits are not very
interesting.  Other times, however (for example when returning cr0 to
userspace), they are, so get the fresh contents of these bits from the guest
by means of a new arch operation.

Signed-off-by: Avi Kivity <avi@qumranet.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index c55635ddf426..aaa98e3e9caf 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -737,6 +737,15 @@ static void exit_lmode(struct kvm_vcpu *vcpu)
 
 #endif
 
+static void vmx_decache_cr0_cr4_guest_bits(struct kvm_vcpu *vcpu)
+{
+        vcpu->cr0 &= KVM_GUEST_CR0_MASK;
+        vcpu->cr0 |= vmcs_readl(GUEST_CR0) & ~KVM_GUEST_CR0_MASK;
+
+        vcpu->cr4 &= KVM_GUEST_CR4_MASK;
+        vcpu->cr4 |= vmcs_readl(GUEST_CR4) & ~KVM_GUEST_CR4_MASK;
+}
+
 static void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 {
         if (vcpu->rmode.active && (cr0 & CR0_PE_MASK))
@@ -2002,6 +2011,7 @@ static struct kvm_arch_ops vmx_arch_ops = {
         .get_segment = vmx_get_segment,
         .set_segment = vmx_set_segment,
         .get_cs_db_l_bits = vmx_get_cs_db_l_bits,
+        .decache_cr0_cr4_guest_bits = vmx_decache_cr0_cr4_guest_bits,
         .set_cr0 = vmx_set_cr0,
         .set_cr0_no_modeswitch = vmx_set_cr0_no_modeswitch,
         .set_cr3 = vmx_set_cr3,