Re: [PATCH v2 3/3] KVM: nSVM: call KVM_REQ_GET_NESTED_STATE_PAGES on exit from SMM mode

Maxim Levitsky
2021-09-12T10:36:26Z

On Thu, 2021-09-09 at 00:59 +0000, Sean Christopherson wrote:
> On Mon, Aug 23, 2021, Maxim Levitsky wrote:
> > This allows nested SVM code to be more similar to nested VMX code.
> >
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> > arch/x86/kvm/svm/nested.c | 9 ++++++---
> > arch/x86/kvm/svm/svm.c | 8 +++++++-
> > arch/x86/kvm/svm/svm.h | 3 ++-
> > 3 files changed, 15 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > index 5e13357da21e..678fd21f6077 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -572,7 +572,7 @@ static void nested_svm_copy_common_state(struct vmcb *from_vmcb, struct vmcb *to
> > }
> >
> > int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
> > - struct vmcb *vmcb12)
> > + struct vmcb *vmcb12, bool from_entry)
>
> from_vmrun would be a better name. VMX uses the slightly absstract from_vmentry
> because of the VMLAUNCH vs. VMRESUME silliness. If we want to explicitly follow
> VMX then from_vmentry would be more appropriate, but I don't see any reason not
> to be more precise.
OK.

>
> > {
> > struct vcpu_svm *svm = to_svm(vcpu);
> > int ret;
> > @@ -602,13 +602,16 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
> > nested_vmcb02_prepare_save(svm, vmcb12);
> >
> > ret = nested_svm_load_cr3(&svm->vcpu, vmcb12->save.cr3,
> > - nested_npt_enabled(svm), true);
> > + nested_npt_enabled(svm), from_entry);
> > if (ret)
> > return ret;
> >
> > if (!npt_enabled)
> > vcpu->arch.mmu->inject_page_fault = svm_inject_page_fault_nested;
> >
> > + if (!from_entry)
> > + kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
> > +
> > svm_set_gif(svm, true);
> >
> > return 0;
> > @@ -674,7 +677,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
> >
> > svm->nested.nested_run_pending = 1;
> >
> > - if (enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12))
> > + if (enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12, true))
> > goto out_exit_err;
> >
> > if (nested_svm_vmrun_msrpm(svm))
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index ea7a4dacd42f..76ee15af8c48 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -4354,6 +4354,12 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
> > if (svm_allocate_nested(svm))
> > return 1;
> >
> > + /* Exit from the SMM to the non root mode also uses
> > + * the KVM_REQ_GET_NESTED_STATE_PAGES request,
> > + * but in this case the pdptrs must be always reloaded
> > + */
> > + vcpu->arch.pdptrs_from_userspace = false;
>
> Hmm, I think this belongs in the previous patch. And I would probably go so far
> as to say it belongs in emulator_leave_smm(), i.e. pdptrs_from_userspace should
> be cleared on RSM regardless of what mode is being resumed.

I actually don't think that this belongs to a previous patch, since this issue didn't exist on SVM,
since it didn't call the KVM_REQ_GET_NESTED_STATE_PAGES.

However I do agree with you that it makes sense to move this hack to the common x86 code.
I had put it to kvm_smm_changed, and will soon send a new version.

>
> > +
> > /*
> > * Restore L1 host state from L1 HSAVE area as VMCB01 was
> > * used during SMM (see svm_enter_smm())
> > @@ -4368,7 +4374,7 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
> >
> > vmcb12 = map.hva;
> > nested_load_control_from_vmcb12(svm, &vmcb12->control);
> > - ret = enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12);
> > + ret = enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12, false);
> >
> > kvm_vcpu_unmap(vcpu, &map, true);
> > kvm_vcpu_unmap(vcpu, &map_save, true);
> > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> > index 524d943f3efc..51ffa46ab257 100644
> > --- a/arch/x86/kvm/svm/svm.h
> > +++ b/arch/x86/kvm/svm/svm.h
> > @@ -459,7 +459,8 @@ static inline bool nested_exit_on_nmi(struct vcpu_svm *svm)
> > return vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_NMI);
> > }
> >
> > -int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb_gpa, struct vmcb *vmcb12);
> > +int enter_svm_guest_mode(struct kvm_vcpu *vcpu,
> > + u64 vmcb_gpa, struct vmcb *vmcb12, bool from_entry);
>
> Alignment is funky, it can/should match the definition, e.g.
Oops, forgot to check the prototype - these things you write once and forget about them,
as long as it compiles :-)

>
> int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
> struct vmcb *vmcb12, bool from_entry);
>
> > void svm_leave_nested(struct vcpu_svm *svm);
> > void svm_free_nested(struct vcpu_svm *svm);
> > int svm_allocate_nested(struct vcpu_svm *svm);
> > --
> > 2.26.3
> >

Thanks for the review!

Best regards,
Maxim Levitsky