When L2 tries to modify CR0 or CR4 (with mov or clts), and modifies a bit
which L1 asked to shadow (via CR[04]_GUEST_HOST_MASK), we already do the right
thing: we let L1 handle the trap (see nested_vmx_exit_handled_cr() in a
previous patch).
When L2 modifies bits that L1 doesn't care about, we let it think (via
CR[04]_READ_SHADOW) that it did these modifications, while only changing
(in GUEST_CR[04]) the bits that L0 doesn't shadow.
This is needed for corect handling of CR0.TS for lazy FPU loading: L0 may
want to leave TS on, while pretending to allow the guest to change it.
Signed-off-by: Nadav Har'El <nyh@xxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 58 ++++++++++++++++++++++++++++++++++++++++---
1 file changed, 55 insertions(+), 3 deletions(-)
--- .before/arch/x86/kvm/vmx.c 2011-05-25 22:41:11.000000000 +0300
+++ .after/arch/x86/kvm/vmx.c 2011-05-25 22:41:11.000000000 +0300
@@ -4163,6 +4163,58 @@ vmx_patch_hypercall(struct kvm_vcpu *vcp
hypercall[2] = 0xc1;
}
+/* called to set cr0 as approriate for a mov-to-cr0 exit. */
+static int handle_set_cr0(struct kvm_vcpu *vcpu, unsigned long val)
+{
+ if (to_vmx(vcpu)->nested.vmxon &&
+ ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON))
+ return 1;
+
+ if (is_guest_mode(vcpu)) {
+ /*
+ * We get here when L2 changed cr0 in a way that did not change
+ * any of L1's shadowed bits (see nested_vmx_exit_handled_cr),
+ * but did change L0 shadowed bits. This can currently happen
+ * with the TS bit: L0 may want to leave TS on (for lazy fpu
+ * loading) while pretending to allow the guest to change it.
+ */
+ if (kvm_set_cr0(vcpu, (val & vcpu->arch.cr0_guest_owned_bits) |
+ (vcpu->arch.cr0 & ~vcpu->arch.cr0_guest_owned_bits)))
+ return 1;
+ vmcs_writel(CR0_READ_SHADOW, val);
+ return 0;
+ } else
+ return kvm_set_cr0(vcpu, val);
+}
+
+static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val)
+{
+ if (is_guest_mode(vcpu)) {
+ if (kvm_set_cr4(vcpu, (val & vcpu->arch.cr4_guest_owned_bits) |
+ (vcpu->arch.cr4 & ~vcpu->arch.cr4_guest_owned_bits)))
+ return 1;
+ vmcs_writel(CR4_READ_SHADOW, val);
+ return 0;
+ } else
+ return kvm_set_cr4(vcpu, val);
+}
+
+/* called to set cr0 as approriate for clts instruction exit. */
+static void handle_clts(struct kvm_vcpu *vcpu)
+{
+ if (is_guest_mode(vcpu)) {
+ /*
+ * We get here when L2 did CLTS, and L1 didn't shadow CR0.TS
+ * but we did (!fpu_active). We need to keep GUEST_CR0.TS on,
+ * just pretend it's off (also in arch.cr0 for fpu_activate).
+ */
+ vmcs_writel(CR0_READ_SHADOW,
+ vmcs_readl(CR0_READ_SHADOW) & ~X86_CR0_TS);
+ vcpu->arch.cr0 &= ~X86_CR0_TS;
+ } else
+ vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
+}
+
static int handle_cr(struct kvm_vcpu *vcpu)
{
unsigned long exit_qualification, val;
@@ -4179,7 +4231,7 @@ static int handle_cr(struct kvm_vcpu *vc
trace_kvm_cr_write(cr, val);
switch (cr) {
case 0:
- err = kvm_set_cr0(vcpu, val);
+ err = handle_set_cr0(vcpu, val);
kvm_complete_insn_gp(vcpu, err);
return 1;
case 3:
@@ -4187,7 +4239,7 @@ static int handle_cr(struct kvm_vcpu *vc
kvm_complete_insn_gp(vcpu, err);
return 1;
case 4:
- err = kvm_set_cr4(vcpu, val);
+ err = handle_set_cr4(vcpu, val);
kvm_complete_insn_gp(vcpu, err);
return 1;
case 8: {
@@ -4205,7 +4257,7 @@ static int handle_cr(struct kvm_vcpu *vc
};
break;
case 2: /* clts */
- vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
+ handle_clts(vcpu);
trace_kvm_cr_write(0, kvm_read_cr0(vcpu));
skip_emulated_instruction(vcpu);
vmx_fpu_activate(vcpu);
--
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