On Tue, Aug 06, 2013 at 10:39:59AM +0200, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>
> If nested EPT is enabled, the L2 guest may change CR3 without any exits.
> We therefore have to read the current value from the VMCS when switching
> to L1. However, if paging wasn't enabled, L0 tracks L2's CR3, and
> GUEST_CR3 rather contains the real-mode identity map. So we need to
> retrieve CR3 from the architectural state after conditionally updating
> it - and this is what kvm_read_cr3 does.
>
I have a headache from trying to think about it already, but shouldn't
L1 be the one who setups identity map for L2? I traced what
vmcs_read64(GUEST_CR3)/kvm_read_cr3(vcpu) return here and do not see
different values in real mode.
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index b482d47..09666aa 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8106,7 +8106,7 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
> * Additionally, restore L2's PDPTR to vmcs12.
> */
> if (enable_ept) {
> - vmcs12->guest_cr3 = vmcs_read64(GUEST_CR3);
> + vmcs12->guest_cr3 = kvm_read_cr3(vcpu);
> vmcs12->guest_pdptr0 = vmcs_read64(GUEST_PDPTR0);
> vmcs12->guest_pdptr1 = vmcs_read64(GUEST_PDPTR1);
> vmcs12->guest_pdptr2 = vmcs_read64(GUEST_PDPTR2);
> --
> 1.7.3.4
--
Gleb.
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