On Tue, Aug 06, 2013 at 12:25:55PM +0200, Jan Kiszka wrote:
> On 2013-08-06 12:12, Gleb Natapov wrote:
> > 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.
>
> Did you try with my patches applied and unrestricted guest mode in use?
>
No, for that I need to setup nested environment on the machine that
support unrestricted guest first :)
> Jan
>
> >
> >> 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.
> >
>
>
--
Gleb.
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