This patch allows the guest to enable the VMXE bit in CR4, which is a
prerequisite to running VMXON.
Whether to allow setting the VMXE bit now depends on the architecture (svm
or vmx), so its checking has moved to kvm_x86_ops->set_cr4(). This function
now returns an int: If kvm_x86_ops->set_cr4() returns 1, __kvm_set_cr4()
will also return 1, and this will cause kvm_set_cr4() will throw a #GP.
Turning on the VMXE bit is allowed only when the nested VMX feature is
enabled, and turning it off is forbidden after a vmxon.
Signed-off-by: Nadav Har'El <nyh@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/svm.c | 6 +++++-
arch/x86/kvm/vmx.c | 17 +++++++++++++++--
arch/x86/kvm/x86.c | 4 +---
4 files changed, 22 insertions(+), 7 deletions(-)
--- .before/arch/x86/include/asm/kvm_host.h 2011-05-16 22:36:46.000000000 +0300
+++ .after/arch/x86/include/asm/kvm_host.h 2011-05-16 22:36:46.000000000 +0300
@@ -559,7 +559,7 @@ struct kvm_x86_ops {
void (*decache_cr4_guest_bits)(struct kvm_vcpu *vcpu);
void (*set_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
void (*set_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);
- void (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
+ int (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
void (*set_efer)(struct kvm_vcpu *vcpu, u64 efer);
void (*get_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
void (*set_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
--- .before/arch/x86/kvm/svm.c 2011-05-16 22:36:46.000000000 +0300
+++ .after/arch/x86/kvm/svm.c 2011-05-16 22:36:46.000000000 +0300
@@ -1496,11 +1496,14 @@ static void svm_set_cr0(struct kvm_vcpu
update_cr0_intercept(svm);
}
-static void svm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+static int svm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
unsigned long host_cr4_mce = read_cr4() & X86_CR4_MCE;
unsigned long old_cr4 = to_svm(vcpu)->vmcb->save.cr4;
+ if (cr4 & X86_CR4_VMXE)
+ return 1;
+
if (npt_enabled && ((old_cr4 ^ cr4) & X86_CR4_PGE))
svm_flush_tlb(vcpu);
@@ -1510,6 +1513,7 @@ static void svm_set_cr4(struct kvm_vcpu
cr4 |= host_cr4_mce;
to_svm(vcpu)->vmcb->save.cr4 = cr4;
mark_dirty(to_svm(vcpu)->vmcb, VMCB_CR);
+ return 0;
}
static void svm_set_segment(struct kvm_vcpu *vcpu,
--- .before/arch/x86/kvm/x86.c 2011-05-16 22:36:46.000000000 +0300
+++ .after/arch/x86/kvm/x86.c 2011-05-16 22:36:46.000000000 +0300
@@ -615,11 +615,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, u
kvm_read_cr3(vcpu)))
return 1;
- if (cr4 & X86_CR4_VMXE)
+ if (kvm_x86_ops->set_cr4(vcpu, cr4))
return 1;
- kvm_x86_ops->set_cr4(vcpu, cr4);
-
if ((cr4 ^ old_cr4) & pdptr_bits)
kvm_mmu_reset_context(vcpu);
--- .before/arch/x86/kvm/vmx.c 2011-05-16 22:36:46.000000000 +0300
+++ .after/arch/x86/kvm/vmx.c 2011-05-16 22:36:46.000000000 +0300
@@ -2078,7 +2078,7 @@ static void ept_save_pdptrs(struct kvm_v
(unsigned long *)&vcpu->arch.regs_dirty);
}
-static void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
+static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
unsigned long cr0,
@@ -2175,11 +2175,23 @@ static void vmx_set_cr3(struct kvm_vcpu
vmcs_writel(GUEST_CR3, guest_cr3);
}
-static void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
unsigned long hw_cr4 = cr4 | (to_vmx(vcpu)->rmode.vm86_active ?
KVM_RMODE_VM_CR4_ALWAYS_ON : KVM_PMODE_VM_CR4_ALWAYS_ON);
+ if (cr4 & X86_CR4_VMXE) {
+ /*
+ * To use VMXON (and later other VMX instructions), a guest
+ * must first be able to turn on cr4.VMXE (see handle_vmon()).
+ * So basically the check on whether to allow nested VMX
+ * is here.
+ */
+ if (!nested_vmx_allowed(vcpu))
+ return 1;
+ } else if (to_vmx(vcpu)->nested.vmxon)
+ return 1;
+
vcpu->arch.cr4 = cr4;
if (enable_ept) {
if (!is_paging(vcpu)) {
@@ -2192,6 +2204,7 @@ static void vmx_set_cr4(struct kvm_vcpu
vmcs_writel(CR4_READ_SHADOW, cr4);
vmcs_writel(GUEST_CR4, hw_cr4);
+ return 0;
}
static void vmx_get_segment(struct kvm_vcpu *vcpu,
--
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