Re: [PATCH v5 02/14] nEPT: Fix cr3 handling in nested exit and entry

Orit Wasserman
2013-08-01T11:27:40Z

On 07/31/2013 05:48 PM, Gleb Natapov wrote:
> From: Nadav Har'El <nyh@il.ibm.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>
> Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> ---
> arch/x86/kvm/vmx.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 27efa6a..4e98764 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -7595,6 +7595,16 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
> kvm_set_cr3(vcpu, vmcs12->guest_cr3);
> kvm_mmu_reset_context(vcpu);
>
> + /*
> + * L1 may access the L2's PDPTR, so save them to construct vmcs12
> + */
> + 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);
> }
> @@ -7917,6 +7927,22 @@ static 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.
> + *
> + * Additionally, restore L2's PDPTR to vmcs12.
> + */
> + if (enable_ept) {
> + vmcs12->guest_cr3 = vmcs_read64(GUEST_CR3);
> + 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);
> + }
> +
> vmcs12->vm_entry_controls =
> (vmcs12->vm_entry_controls & ~VM_ENTRY_IA32E_MODE) |
> (vmcs_read32(VM_ENTRY_CONTROLS) & VM_ENTRY_IA32E_MODE);
>

Reviewed-by: Orit Wasserman <owasserm@redhat.com>