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

From: Wei Huang
Date: Fri Sep 18 2020 - 17:13:57 EST

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On 09/17 03:23, Cathy Avery wrote:
> 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

I was able to run some basic nested SVM tests using this patch. Full L2 VM
(Fedora) had some problem to boot after grub loading kernel.

Comments below.

>
> 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;

This part is a bit confusing. svm->vmcb01->control contains the control
info from L0 hypervisor to L1 VM. Shouldn't vmcb02->control use the info
from the control info contained in nested_vmcb?

> + 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);
> +
> + /* 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);

We do save some copying time here, which is always a good thing especially
for nested virt.

>
> 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);

Does this mean the original code is missing the following?

else
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;

Any reason that vmcb01_pa can't be placed in "struct vcpu_svm" below, along
with vmcb01?

> + 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;
> }
>
> static inline void set_cr_intercept(struct vcpu_svm *svm, int bit)
> --
> 2.20.1
>

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