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

[Maxim Levitsky]

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@xxxxxxxxxx>
> > ---
> >  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