Re: [PATCH] KVM: SVM: Use a separate vmcb for the nested L2 guest

[Cathy Avery <cavery@xxxxxxxxxx>]

On 9/18/20 11:16 AM, Babu Moger wrote:
> Cathy,
> Thanks for the patches. It cleans up the code nicely.
> But there are some issues with the patch. I was able to bring the L1 guest
> with your patch. But when I tried to load L2 guest it crashed. I am
> thinking It is mostly due to save/restore part of vmcb. Few comments below.
>
> > -----Original Message-----
> > From: Cathy Avery <cavery@xxxxxxxxxx>
> > Sent: Thursday, September 17, 2020 2:23 PM
> > To: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; pbonzini@xxxxxxxxxx
> > Cc: vkuznets@xxxxxxxxxx; Huang2, Wei <Wei.Huang2@xxxxxxx>
> > Subject: [PATCH] KVM: SVM: Use a separate vmcb for the nested L2 guest
> >
> > svm->vmcb will now point to either a separate vmcb L1 ( not nested ) or L2 vmcb
> > ( nested ).
> >
> > Issues:
> >
> > 1) There is some wholesale copying of vmcb.save and vmcb.contol
> >     areas which will need to be refined.
> >
> > 2) There is a workaround in nested_svm_vmexit() where
> >
> >     if (svm->vmcb01->control.asid == 0)
> >         svm->vmcb01->control.asid = svm->nested.vmcb02->control.asid;
> >
> >     This was done as a result of the kvm selftest 'state_test'. In that
> >     test svm_set_nested_state() is called before svm_vcpu_run().
> >     The asid is assigned by svm_vcpu_run -> pre_svm_run for the current
> >     vmcb which is now vmcb02 as we are in nested mode subsequently
> >     vmcb01.control.asid is never set as it should be.
> >
> > Tested:
> > kvm-unit-tests
> > kvm self tests
> >
> > Signed-off-by: Cathy Avery <cavery@xxxxxxxxxx>
> > ---
> >   arch/x86/kvm/svm/nested.c | 116 ++++++++++++++++++--------------------
> >   arch/x86/kvm/svm/svm.c    |  41 +++++++-------
> >   arch/x86/kvm/svm/svm.h    |  10 ++--
> >   3 files changed, 81 insertions(+), 86 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index
> > e90bc436f584..0a06e62010d8 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -75,12 +75,12 @@ static unsigned long nested_svm_get_tdp_cr3(struct
> > kvm_vcpu *vcpu)  static void nested_svm_init_mmu_context(struct kvm_vcpu
> > *vcpu)  {
> >   	struct vcpu_svm *svm = to_svm(vcpu);
> > -	struct vmcb *hsave = svm->nested.hsave;
> >
> >   	WARN_ON(mmu_is_nested(vcpu));
> >
> >   	vcpu->arch.mmu = &vcpu->arch.guest_mmu;
> > -	kvm_init_shadow_npt_mmu(vcpu, X86_CR0_PG, hsave->save.cr4,
> > hsave->save.efer,
> > +	kvm_init_shadow_npt_mmu(vcpu, X86_CR0_PG, svm->vmcb01-
> > > save.cr4,
> > +				svm->vmcb01->save.efer,
> >   				svm->nested.ctl.nested_cr3);
> >   	vcpu->arch.mmu->get_guest_pgd     = nested_svm_get_tdp_cr3;
> >   	vcpu->arch.mmu->get_pdptr         = nested_svm_get_tdp_pdptr;
> > @@ -105,7 +105,7 @@ void recalc_intercepts(struct vcpu_svm *svm)
> >   		return;
> >
> >   	c = &svm->vmcb->control;
> > -	h = &svm->nested.hsave->control;
> > +	h = &svm->vmcb01->control;
> >   	g = &svm->nested.ctl;
> >
> >   	svm->nested.host_intercept_exceptions = h->intercept_exceptions;
> > @@ -403,7 +403,7 @@ static void nested_prepare_vmcb_control(struct
> > vcpu_svm *svm)
> >
> >   	svm->vmcb->control.int_ctl             =
> >   		(svm->nested.ctl.int_ctl & ~mask) |
> > -		(svm->nested.hsave->control.int_ctl & mask);
> > +		(svm->vmcb01->control.int_ctl & mask);
> >
> >   	svm->vmcb->control.virt_ext            = svm->nested.ctl.virt_ext;
> >   	svm->vmcb->control.int_vector          = svm->nested.ctl.int_vector;
> > @@ -432,6 +432,12 @@ int enter_svm_guest_mode(struct vcpu_svm *svm, u64
> > vmcb_gpa,
> >   	int ret;
> >
> >   	svm->nested.vmcb = vmcb_gpa;
> > +
> > +	WARN_ON(svm->vmcb == svm->nested.vmcb02);
> > +
> > +	svm->nested.vmcb02->control = svm->vmcb01->control;
> > +	svm->vmcb = svm->nested.vmcb02;
> > +	svm->vmcb_pa = svm->nested.vmcb02_pa;
> >   	load_nested_vmcb_control(svm, &nested_vmcb->control);
> >   	nested_prepare_vmcb_save(svm, nested_vmcb);
> >   	nested_prepare_vmcb_control(svm);
> > @@ -450,8 +456,6 @@ int nested_svm_vmrun(struct vcpu_svm *svm)  {
> >   	int ret;
> >   	struct vmcb *nested_vmcb;
> > -	struct vmcb *hsave = svm->nested.hsave;
> > -	struct vmcb *vmcb = svm->vmcb;
> >   	struct kvm_host_map map;
> >   	u64 vmcb_gpa;
> >
> > @@ -496,29 +500,17 @@ int nested_svm_vmrun(struct vcpu_svm *svm)
> >   	kvm_clear_exception_queue(&svm->vcpu);
> >   	kvm_clear_interrupt_queue(&svm->vcpu);
> >
> > -	/*
> > -	 * Save the old vmcb, so we don't need to pick what we save, but can
> > -	 * restore everything when a VMEXIT occurs
> > -	 */
> > -	hsave->save.es     = vmcb->save.es;
> > -	hsave->save.cs     = vmcb->save.cs;
> > -	hsave->save.ss     = vmcb->save.ss;
> > -	hsave->save.ds     = vmcb->save.ds;
> > -	hsave->save.gdtr   = vmcb->save.gdtr;
> > -	hsave->save.idtr   = vmcb->save.idtr;
> > -	hsave->save.efer   = svm->vcpu.arch.efer;
> > -	hsave->save.cr0    = kvm_read_cr0(&svm->vcpu);
> > -	hsave->save.cr4    = svm->vcpu.arch.cr4;
> > -	hsave->save.rflags = kvm_get_rflags(&svm->vcpu);
> > -	hsave->save.rip    = kvm_rip_read(&svm->vcpu);
> > -	hsave->save.rsp    = vmcb->save.rsp;
> > -	hsave->save.rax    = vmcb->save.rax;
> > -	if (npt_enabled)
> > -		hsave->save.cr3    = vmcb->save.cr3;
> > -	else
> > -		hsave->save.cr3    = kvm_read_cr3(&svm->vcpu);
> > -
> > -	copy_vmcb_control_area(&hsave->control, &vmcb->control);
> You may have to carefully check the above cleanup.
Thanks I'll check it out. I did not see a crash when running the tests.  
Could you send me more information about your test and test setup, stack 
trace, etc.
> > +
> > +	/* Update vmcb0. We will restore everything when a VMEXIT occurs */
> > +
> > +	svm->vmcb01->save.efer   = svm->vcpu.arch.efer;
> > +	svm->vmcb01->save.cr0    = kvm_read_cr0(&svm->vcpu);
> > +	svm->vmcb01->save.cr4    = svm->vcpu.arch.cr4;
> > +	svm->vmcb01->save.rflags = kvm_get_rflags(&svm->vcpu);
> > +	svm->vmcb01->save.rip    = kvm_rip_read(&svm->vcpu);
> > +
> > +	if (!npt_enabled)
> > +		svm->vmcb01->save.cr3 = kvm_read_cr3(&svm->vcpu);
> >
> >   	svm->nested.nested_run_pending = 1;
> >
> > @@ -564,7 +556,6 @@ int nested_svm_vmexit(struct vcpu_svm *svm)  {
> >   	int rc;
> >   	struct vmcb *nested_vmcb;
> > -	struct vmcb *hsave = svm->nested.hsave;
> >   	struct vmcb *vmcb = svm->vmcb;
> >   	struct kvm_host_map map;
> >
> > @@ -628,8 +619,11 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
> >   	nested_vmcb->control.pause_filter_thresh =
> >   		svm->vmcb->control.pause_filter_thresh;
> >
> > -	/* Restore the original control entries */
> > -	copy_vmcb_control_area(&vmcb->control, &hsave->control);
> > +	if (svm->vmcb01->control.asid == 0)
> > +		svm->vmcb01->control.asid = svm->nested.vmcb02-
> > > control.asid;
> > +
> > +	svm->vmcb = svm->vmcb01;
> > +	svm->vmcb_pa = svm->nested.vmcb01_pa;
> >
> >   	/* On vmexit the  GIF is set to false */
> >   	svm_set_gif(svm, false);
> > @@ -640,19 +634,13 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
> >   	svm->nested.ctl.nested_cr3 = 0;
> >
> >   	/* Restore selected save entries */
> > -	svm->vmcb->save.es = hsave->save.es;
> > -	svm->vmcb->save.cs = hsave->save.cs;
> > -	svm->vmcb->save.ss = hsave->save.ss;
> > -	svm->vmcb->save.ds = hsave->save.ds;
> > -	svm->vmcb->save.gdtr = hsave->save.gdtr;
> > -	svm->vmcb->save.idtr = hsave->save.idtr;
> > -	kvm_set_rflags(&svm->vcpu, hsave->save.rflags);
> > -	svm_set_efer(&svm->vcpu, hsave->save.efer);
> > -	svm_set_cr0(&svm->vcpu, hsave->save.cr0 | X86_CR0_PE);
> > -	svm_set_cr4(&svm->vcpu, hsave->save.cr4);
> > -	kvm_rax_write(&svm->vcpu, hsave->save.rax);
> > -	kvm_rsp_write(&svm->vcpu, hsave->save.rsp);
> > -	kvm_rip_write(&svm->vcpu, hsave->save.rip);
> > +	kvm_set_rflags(&svm->vcpu, svm->vmcb->save.rflags);
> > +	svm_set_efer(&svm->vcpu, svm->vmcb->save.efer);
> > +	svm_set_cr0(&svm->vcpu, svm->vmcb->save.cr0 | X86_CR0_PE);
> > +	svm_set_cr4(&svm->vcpu, svm->vmcb->save.cr4);
> > +	kvm_rax_write(&svm->vcpu, svm->vmcb->save.rax);
> > +	kvm_rsp_write(&svm->vcpu, svm->vmcb->save.rsp);
> > +	kvm_rip_write(&svm->vcpu, svm->vmcb->save.rip);
> >   	svm->vmcb->save.dr7 = 0;
> >   	svm->vmcb->save.cpl = 0;
> >   	svm->vmcb->control.exit_int_info = 0;
> > @@ -670,12 +658,12 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
> >
> >   	nested_svm_uninit_mmu_context(&svm->vcpu);
> >
> > -	rc = nested_svm_load_cr3(&svm->vcpu, hsave->save.cr3, false);
> > +	rc = nested_svm_load_cr3(&svm->vcpu, svm->vmcb->save.cr3, false);
> >   	if (rc)
> >   		return 1;
> >
> > -	if (npt_enabled)
> > -		svm->vmcb->save.cr3 = hsave->save.cr3;
> > +	if (!npt_enabled)
> > +		svm->vmcb01->save.cr3 = kvm_read_cr3(&svm->vcpu);
> >
> >   	/*
> >   	 * Drop what we picked up for L2 via svm_complete_interrupts() so it
> > @@ -694,12 +682,10 @@ int nested_svm_vmexit(struct vcpu_svm *svm)  void
> > svm_leave_nested(struct vcpu_svm *svm)  {
> >   	if (is_guest_mode(&svm->vcpu)) {
> > -		struct vmcb *hsave = svm->nested.hsave;
> > -		struct vmcb *vmcb = svm->vmcb;
> > -
> >   		svm->nested.nested_run_pending = 0;
> >   		leave_guest_mode(&svm->vcpu);
> > -		copy_vmcb_control_area(&vmcb->control, &hsave->control);
> > +		svm->vmcb = svm->vmcb01;
> > +		svm->vmcb_pa = svm->nested.vmcb01_pa;
> >   		nested_svm_uninit_mmu_context(&svm->vcpu);
> >   	}
> >   }
> > @@ -1046,10 +1032,9 @@ static int svm_get_nested_state(struct kvm_vcpu
> > *vcpu,
> >   	if (copy_to_user(&user_vmcb->control, &svm->nested.ctl,
> >   			 sizeof(user_vmcb->control)))
> >   		return -EFAULT;
> > -	if (copy_to_user(&user_vmcb->save, &svm->nested.hsave->save,
> > +	if (copy_to_user(&user_vmcb->save, &svm->vmcb01->save,
> >   			 sizeof(user_vmcb->save)))
> >   		return -EFAULT;
> > -
> >   out:
> >   	return kvm_state.size;
> >   }
> > @@ -1059,7 +1044,6 @@ static int svm_set_nested_state(struct kvm_vcpu
> > *vcpu,
> >   				struct kvm_nested_state *kvm_state)  {
> >   	struct vcpu_svm *svm = to_svm(vcpu);
> > -	struct vmcb *hsave = svm->nested.hsave;
> >   	struct vmcb __user *user_vmcb = (struct vmcb __user *)
> >   		&user_kvm_nested_state->data.svm[0];
> >   	struct vmcb_control_area ctl;
> > @@ -1121,16 +1105,24 @@ static int svm_set_nested_state(struct kvm_vcpu
> > *vcpu,
> >   	if (!(save.cr0 & X86_CR0_PG))
> >   		return -EINVAL;
> >
> > +	svm->nested.vmcb02->control = svm->vmcb01->control;
> > +	svm->nested.vmcb02->save = svm->vmcb01->save;
> > +	svm->vmcb01->save = save;
> > +
> > +	WARN_ON(svm->vmcb == svm->nested.vmcb02);
> > +
> > +	svm->nested.vmcb = kvm_state->hdr.svm.vmcb_pa;
> > +
> > +	svm->vmcb = svm->nested.vmcb02;
> > +	svm->vmcb_pa = svm->nested.vmcb02_pa;
> > +
> >   	/*
> > -	 * All checks done, we can enter guest mode.  L1 control fields
> > -	 * come from the nested save state.  Guest state is already
> > -	 * in the registers, the save area of the nested state instead
> > -	 * contains saved L1 state.
> > +	 * All checks done, we can enter guest mode. L2 control fields will
> > +	 * be the result of a combination of L1 and userspace indicated
> > +	 * L12.control. The save area of L1 vmcb now contains the userspace
> > +	 * indicated L1.save.
> >   	 */
> > -	copy_vmcb_control_area(&hsave->control, &svm->vmcb->control);
> > -	hsave->save = save;
> >
> > -	svm->nested.vmcb = kvm_state->hdr.svm.vmcb_pa;
> >   	load_nested_vmcb_control(svm, &ctl);
> >   	nested_prepare_vmcb_control(svm);
> >
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index
> > 5764b87379cf..d8022f989ffb 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -971,8 +971,8 @@ static u64 svm_write_l1_tsc_offset(struct kvm_vcpu
> > *vcpu, u64 offset)
> >   	if (is_guest_mode(vcpu)) {
> >   		/* Write L1's TSC offset.  */
> >   		g_tsc_offset = svm->vmcb->control.tsc_offset -
> > -			       svm->nested.hsave->control.tsc_offset;
> > -		svm->nested.hsave->control.tsc_offset = offset;
> > +			       svm->vmcb01->control.tsc_offset;
> > +		svm->vmcb01->control.tsc_offset = offset;
> >   	}
> >
> >   	trace_kvm_write_tsc_offset(vcpu->vcpu_id,
> > @@ -1171,9 +1171,9 @@ static void svm_vcpu_reset(struct kvm_vcpu *vcpu,
> > bool init_event)  static int svm_create_vcpu(struct kvm_vcpu *vcpu)  {
> >   	struct vcpu_svm *svm;
> > -	struct page *page;
> > +	struct page *vmcb01_page;
> > +	struct page *vmcb02_page;
> >   	struct page *msrpm_pages;
> > -	struct page *hsave_page;
> >   	struct page *nested_msrpm_pages;
> >   	int err;
> >
> > @@ -1181,8 +1181,8 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
> >   	svm = to_svm(vcpu);
> >
> >   	err = -ENOMEM;
> > -	page = alloc_page(GFP_KERNEL_ACCOUNT);
> > -	if (!page)
> > +	vmcb01_page = alloc_page(GFP_KERNEL_ACCOUNT);
> > +	if (!vmcb01_page)
> >   		goto out;
> >
> >   	msrpm_pages = alloc_pages(GFP_KERNEL_ACCOUNT,
> > MSRPM_ALLOC_ORDER); @@ -1193,8 +1193,8 @@ static int
> > svm_create_vcpu(struct kvm_vcpu *vcpu)
> >   	if (!nested_msrpm_pages)
> >   		goto free_page2;
> >
> > -	hsave_page = alloc_page(GFP_KERNEL_ACCOUNT);
> > -	if (!hsave_page)
> > +	vmcb02_page = alloc_page(GFP_KERNEL_ACCOUNT);
> > +	if (!vmcb02_page)
> >   		goto free_page3;
> >
> >   	err = avic_init_vcpu(svm);
> > @@ -1207,8 +1207,9 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
> >   	if (irqchip_in_kernel(vcpu->kvm) && kvm_apicv_activated(vcpu->kvm))
> >   		svm->avic_is_running = true;
> >
> > -	svm->nested.hsave = page_address(hsave_page);
> > -	clear_page(svm->nested.hsave);
> > +	svm->nested.vmcb02 = page_address(vmcb02_page);
> > +	clear_page(svm->nested.vmcb02);
> > +	svm->nested.vmcb02_pa = __sme_set(page_to_pfn(vmcb02_page) <<
> > +PAGE_SHIFT);
> >
> >   	svm->msrpm = page_address(msrpm_pages);
> >   	svm_vcpu_init_msrpm(svm->msrpm);
> > @@ -1216,9 +1217,11 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
> >   	svm->nested.msrpm = page_address(nested_msrpm_pages);
> >   	svm_vcpu_init_msrpm(svm->nested.msrpm);
> >
> > -	svm->vmcb = page_address(page);
> > +	svm->vmcb = svm->vmcb01 = page_address(vmcb01_page);
> >   	clear_page(svm->vmcb);
> > -	svm->vmcb_pa = __sme_set(page_to_pfn(page) << PAGE_SHIFT);
> > +	svm->vmcb_pa = __sme_set(page_to_pfn(vmcb01_page) <<
> > PAGE_SHIFT);
> > +	svm->nested.vmcb01_pa = svm->vmcb_pa;
> > +
> >   	svm->asid_generation = 0;
> >   	init_vmcb(svm);
> >
> > @@ -1228,13 +1231,13 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
> >   	return 0;
> >
> >   free_page4:
> > -	__free_page(hsave_page);
> > +	__free_page(vmcb02_page);
> >   free_page3:
> >   	__free_pages(nested_msrpm_pages, MSRPM_ALLOC_ORDER);
> >   free_page2:
> >   	__free_pages(msrpm_pages, MSRPM_ALLOC_ORDER);
> >   free_page1:
> > -	__free_page(page);
> > +	__free_page(vmcb01_page);
> >   out:
> >   	return err;
> >   }
> > @@ -1256,11 +1259,11 @@ static void svm_free_vcpu(struct kvm_vcpu *vcpu)
> >   	 * svm_vcpu_load(). So, ensure that no logical CPU has this
> >   	 * vmcb page recorded as its current vmcb.
> >   	 */
> > -	svm_clear_current_vmcb(svm->vmcb);
> >
> > -	__free_page(pfn_to_page(__sme_clr(svm->vmcb_pa) >> PAGE_SHIFT));
> > +	svm_clear_current_vmcb(svm->vmcb);
> > +	__free_page(pfn_to_page(__sme_clr(svm->nested.vmcb01_pa) >>
> > PAGE_SHIFT));
> > +	__free_page(pfn_to_page(__sme_clr(svm->nested.vmcb02_pa) >>
> > +PAGE_SHIFT));
> >   	__free_pages(virt_to_page(svm->msrpm), MSRPM_ALLOC_ORDER);
> > -	__free_page(virt_to_page(svm->nested.hsave));
> >   	__free_pages(virt_to_page(svm->nested.msrpm),
> > MSRPM_ALLOC_ORDER);  }
> >
> > @@ -1393,7 +1396,7 @@ static void svm_clear_vintr(struct vcpu_svm *svm)
> >   	/* Drop int_ctl fields related to VINTR injection.  */
> >   	svm->vmcb->control.int_ctl &= mask;
> >   	if (is_guest_mode(&svm->vcpu)) {
> > -		svm->nested.hsave->control.int_ctl &= mask;
> > +		svm->vmcb01->control.int_ctl &= mask;
> >
> >   		WARN_ON((svm->vmcb->control.int_ctl & V_TPR_MASK) !=
> >   			(svm->nested.ctl.int_ctl & V_TPR_MASK)); @@ -3127,7
> > +3130,7 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
> >   	if (is_guest_mode(vcpu)) {
> >   		/* As long as interrupts are being delivered...  */
> >   		if ((svm->nested.ctl.int_ctl & V_INTR_MASKING_MASK)
> > -		    ? !(svm->nested.hsave->save.rflags & X86_EFLAGS_IF)
> > +		    ? !(svm->vmcb01->save.rflags & X86_EFLAGS_IF)
> >   		    : !(kvm_get_rflags(vcpu) & X86_EFLAGS_IF))
> >   			return true;
> >
> > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index
> > a798e1731709..e908b83bfa69 100644
> > --- a/arch/x86/kvm/svm/svm.h
> > +++ b/arch/x86/kvm/svm/svm.h
> > @@ -82,7 +82,9 @@ struct kvm_svm {
> >   struct kvm_vcpu;
> >
> >   struct svm_nested_state {
> > -	struct vmcb *hsave;
> > +	struct vmcb *vmcb02;
> > +	unsigned long vmcb01_pa;
> > +	unsigned long vmcb02_pa;
> >   	u64 hsave_msr;
> >   	u64 vm_cr_msr;
> >   	u64 vmcb;
> > @@ -102,6 +104,7 @@ struct svm_nested_state {  struct vcpu_svm {
> >   	struct kvm_vcpu vcpu;
> >   	struct vmcb *vmcb;
> > +	struct vmcb *vmcb01;
> >   	unsigned long vmcb_pa;
> >   	struct svm_cpu_data *svm_data;
> >   	uint64_t asid_generation;
> > @@ -208,10 +211,7 @@ static inline struct vcpu_svm *to_svm(struct kvm_vcpu
> > *vcpu)
> >
> >   static inline struct vmcb *get_host_vmcb(struct vcpu_svm *svm)  {
> > -	if (is_guest_mode(&svm->vcpu))
> > -		return svm->nested.hsave;
> > -	else
> > -		return svm->vmcb;
> > +	return svm->vmcb01;
> Shouldn't it return svm->vmcb? That is what your commit message says.
I believe this is correct. The function is designed to return the host 
vmcb which will always be vmcb01.
> >   }
> >
> >   static inline void set_cr_intercept(struct vcpu_svm *svm, int bit)
> > --
> > 2.20.1