On Thu, Jun 06, 2019 at 02:22:56PM +0200, Paolo Bonzini wrote:
> On 20/05/19 22:10, Sean Christopherson wrote:
> > @@ -3777,18 +3777,8 @@ static void nested_vmx_restore_host_state(struct kvm_vcpu *vcpu)
> > vmx_set_cr4(vcpu, vmcs_readl(CR4_READ_SHADOW));
> >
> > nested_ept_uninit_mmu_context(vcpu);
> > -
> > - /*
> > - * This is only valid if EPT is in use, otherwise the vmcs01 GUEST_CR3
> > - * points to shadow pages! Fortunately we only get here after a WARN_ON
> > - * if EPT is disabled, so a VMabort is perfectly fine.
> > - */
> > - if (enable_ept) {
> > - vcpu->arch.cr3 = vmcs_readl(GUEST_CR3);
> > - __set_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail);
> > - } else {
> > - nested_vmx_abort(vcpu, VMX_ABORT_VMCS_CORRUPTED);
> > - }
> > + vcpu->arch.cr3 = vmcs_readl(GUEST_CR3);
> > + __set_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail);
> >
> > /*
> > * Use ept_save_pdptrs(vcpu) to load the MMU's cached PDPTRs
>
> This hunk needs to be moved to patch 1, which then becomes much easier
> to understand...
I kept the revert in a separate patch so that the bug fix could be
easily backported to stable branches (commit 2b27924bb1d4 ("KVM: nVMX:
always use early vmcs check when EPT is disabled" wasn't tagged for
stable).
> I'm still missing however the place where kvm_mmu_new_cr3 is called
> in the nested_vmx_restore_host_state path.
vcpu->arch.root_mmu.root_hpa is set to INVALID_PAGE via:
nested_vmx_restore_host_state() ->
kvm_mmu_reset_context() ->
kvm_mmu_unload() ->
kvm_mmu_free_roots()
kvm_mmu_unload() has WARN_ON(root_hpa != INVALID_PAGE), i.e. we can bank
on 'root_hpa == INVALID_PAGE' unless the implementation of
kvm_mmu_reset_context() is changed.
On the way into L1, VMCS.GUEST_CR3 is guaranteed to be written (on a
successful entry) via:
vcpu_enter_guest() ->
kvm_mmu_reload() ->
kvm_mmu_load() ->
kvm_mmu_load_cr3() ->
vmx_set_cr3()
The optimization in kvm_mmu_reload() will fail because kvm_mmu_unload()
set vcpu->arch.root_mmu.root_hpa=INVALID_PAGE, and vcpu->arch.mmu is
guaranteed to point at root_mmu (via nested_ept_uninit_mmu_context()).
