This patch allows a guest to use the VMXON and VMXOFF instructions, and
emulates them accordingly. Basically this amounts to checking some
prerequisites, and then remembering whether the guest has enabled or disabled
VMX operation.
Signed-off-by: Nadav Har'El <nyh@xxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 102 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 100 insertions(+), 2 deletions(-)
--- .before/arch/x86/kvm/vmx.c 2010-10-17 11:52:00.000000000 +0200
+++ .after/arch/x86/kvm/vmx.c 2010-10-17 11:52:00.000000000 +0200
@@ -127,6 +127,17 @@ struct shared_msr_entry {
u64 mask;
};
+/*
+ * The nested_vmx structure is part of vcpu_vmx, and holds information we need
+ * for correct emulation of VMX (i.e., nested VMX) on this vcpu. For example,
+ * the current VMCS set by L1, a list of the VMCSs used to run the active
+ * L2 guests on the hardware, and more.
+ */
+struct nested_vmx {
+ /* Has the level1 guest done vmxon? */
+ bool vmxon;
+};
+
struct vcpu_vmx {
struct kvm_vcpu vcpu;
struct list_head local_vcpus_link;
@@ -174,6 +185,9 @@ struct vcpu_vmx {
u32 exit_reason;
bool rdtscp_enabled;
+
+ /* Support for a guest hypervisor (nested VMX) */
+ struct nested_vmx nested;
};
static inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)
@@ -3364,6 +3378,90 @@ static int handle_vmx_insn(struct kvm_vc
return 1;
}
+/*
+ * Emulate the VMXON instruction.
+ * Currently, we just remember that VMX is active, and do not save or even
+ * inspect the argument to VMXON (the so-called "VMXON pointer") because we
+ * do not currently need to store anything in that guest-allocated memory
+ * region. Consequently, VMCLEAR and VMPTRLD also do not verify that the their
+ * argument is different from the VMXON pointer (which the spec says they do).
+ */
+static int handle_vmon(struct kvm_vcpu *vcpu)
+{
+ struct kvm_segment cs;
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+ /* The Intel VMX Instruction Reference lists a bunch of bits that
+ * are prerequisite to running VMXON, most notably CR4.VMXE must be
+ * set to 1. Otherwise, we should fail with #UD. We test these now:
+ */
+ if (!nested ||
+ !kvm_read_cr4_bits(vcpu, X86_CR4_VMXE) ||
+ !kvm_read_cr0_bits(vcpu, X86_CR0_PE) ||
+ (vmx_get_rflags(vcpu) & X86_EFLAGS_VM)) {
+ kvm_queue_exception(vcpu, UD_VECTOR);
+ return 1;
+ }
+
+ vmx_get_segment(vcpu, &cs, VCPU_SREG_CS);
+ if (is_long_mode(vcpu) && !cs.l) {
+ kvm_queue_exception(vcpu, UD_VECTOR);
+ return 1;
+ }
+
+ if (vmx_get_cpl(vcpu)) {
+ kvm_inject_gp(vcpu, 0);
+ return 1;
+ }
+
+ vmx->nested.vmxon = true;
+
+ skip_emulated_instruction(vcpu);
+ return 1;
+}
+
+/*
+ * Intel's VMX Instruction Reference specifies a common set of prerequisites
+ * for running VMX instructions (except VMXON, whose prerequisites are
+ * slightly different). It also specifies what exception to inject otherwise.
+ */
+static int nested_vmx_check_permission(struct kvm_vcpu *vcpu)
+{
+ struct kvm_segment cs;
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+ if (!vmx->nested.vmxon) {
+ kvm_queue_exception(vcpu, UD_VECTOR);
+ return 0;
+ }
+
+ vmx_get_segment(vcpu, &cs, VCPU_SREG_CS);
+ if ((vmx_get_rflags(vcpu) & X86_EFLAGS_VM) ||
+ (is_long_mode(vcpu) && !cs.l)) {
+ kvm_queue_exception(vcpu, UD_VECTOR);
+ return 0;
+ }
+
+ if (vmx_get_cpl(vcpu)) {
+ kvm_inject_gp(vcpu, 0);
+ return 0;
+ }
+
+ return 1;
+}
+
+/* Emulate the VMXOFF instruction */
+static int handle_vmoff(struct kvm_vcpu *vcpu)
+{
+ if (!nested_vmx_check_permission(vcpu))
+ return 1;
+
+ to_vmx(vcpu)->nested.vmxon = false;
+
+ skip_emulated_instruction(vcpu);
+ return 1;
+}
+
static int handle_invlpg(struct kvm_vcpu *vcpu)
{
unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
@@ -3673,8 +3771,8 @@ static int (*kvm_vmx_exit_handlers[])(st
[EXIT_REASON_VMREAD] = handle_vmx_insn,
[EXIT_REASON_VMRESUME] = handle_vmx_insn,
[EXIT_REASON_VMWRITE] = handle_vmx_insn,
- [EXIT_REASON_VMOFF] = handle_vmx_insn,
- [EXIT_REASON_VMON] = handle_vmx_insn,
+ [EXIT_REASON_VMOFF] = handle_vmoff,
+ [EXIT_REASON_VMON] = handle_vmon,
[EXIT_REASON_TPR_BELOW_THRESHOLD] = handle_tpr_below_threshold,
[EXIT_REASON_APIC_ACCESS] = handle_apic_access,
[EXIT_REASON_WBINVD] = handle_wbinvd,
--
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