[PATCH 04/11] nEPT: Fix cr3 handling in nested exit and entry

[Jun Nakajima <jun.nakajima@intel.com>]

The existing code for handling cr3 and related VMCS fields during nested
exit and entry wasn't correct in all cases:

If L2 is allowed to control cr3 (and this is indeed the case in nested EPT),
during nested exit we must copy the modified cr3 from vmcs02 to vmcs12, and
we forgot to do so. This patch adds this copy.

If L0 isn't controlling cr3 when running L2 (i.e., L0 is using EPT), and
whoever does control cr3 (L1 or L2) is using PAE, the processor might have
saved PDPTEs and we should also save them in vmcs12 (and restore later).

Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Signed-off-by: Jun Nakajima <jun.nakajima@intel.com>
Signed-off-by: Xinhao Xu <xinhao.xu@intel.com>
---
 arch/x86/kvm/vmx.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 6ab53ca..26a1b6f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7163,10 +7163,26 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	vmx_set_cr4(vcpu, vmcs12->guest_cr4);
 	vmcs_writel(CR4_READ_SHADOW, nested_read_cr4(vmcs12));
 
-	/* shadow page tables on either EPT or shadow page tables */
+	/*
+	 * Note that kvm_set_cr3() and kvm_mmu_reset_context() will do the
+	 * right thing, and set GUEST_CR3 and/or EPT_POINTER in all supported
+	 * settings: 1. shadow page tables on shadow page tables, 2. shadow
+	 * page tables on EPT, 3. EPT on EPT.
+	 */
 	kvm_set_cr3(vcpu, vmcs12->guest_cr3);
 	kvm_mmu_reset_context(vcpu);
 
+	/*
+	 * Additionally, except when L0 is using shadow page tables, L1 or
+	 * L2 control guest_cr3 for L2, so they may also have saved PDPTEs
+	 */
+	if (enable_ept) {
+		vmcs_write64(GUEST_PDPTR0, vmcs12->guest_pdptr0);
+		vmcs_write64(GUEST_PDPTR1, vmcs12->guest_pdptr1);
+		vmcs_write64(GUEST_PDPTR2, vmcs12->guest_pdptr2);
+		vmcs_write64(GUEST_PDPTR3, vmcs12->guest_pdptr3);
+	}
+
 	kvm_register_write(vcpu, VCPU_REGS_RSP, vmcs12->guest_rsp);
 	kvm_register_write(vcpu, VCPU_REGS_RIP, vmcs12->guest_rip);
 }
@@ -7398,6 +7414,25 @@ void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	vmcs12->guest_pending_dbg_exceptions =
 		vmcs_readl(GUEST_PENDING_DBG_EXCEPTIONS);
 
+	/*
+	 * In some cases (usually, nested EPT), L2 is allowed to change its
+	 * own CR3 without exiting. If it has changed it, we must keep it.
+	 * Of course, if L0 is using shadow page tables, GUEST_CR3 was defined
+	 * by L0, not L1 or L2, so we mustn't unconditionally copy it to vmcs12.
+	 */
+	if (enable_ept)
+		vmcs12->guest_cr3 = vmcs_read64(GUEST_CR3);
+	/*
+	 * Additionally, except when L0 is using shadow page tables, L1 or
+	 * L2 control guest_cr3 for L2, so save their PDPTEs
+	 */
+	if (enable_ept) {
+		vmcs12->guest_pdptr0 = vmcs_read64(GUEST_PDPTR0);
+		vmcs12->guest_pdptr1 = vmcs_read64(GUEST_PDPTR1);
+		vmcs12->guest_pdptr2 = vmcs_read64(GUEST_PDPTR2);
+		vmcs12->guest_pdptr3 = vmcs_read64(GUEST_PDPTR3);
+	}
+
 	/* TODO: These cannot have changed unless we have MSR bitmaps and
 	 * the relevant bit asks not to trap the change */
 	vmcs12->guest_ia32_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL);
-- 
1.8.2.1.610.g562af5b