Re: [PATCH v3 7/8] nSVM: use vmcb_ctrl_area_cached instead of vmcb_control_area in struct svm_nested_state

Maxim Levitsky
2021-10-22T14:51:13Z

On Mon, 2021-10-11 at 10:37 -0400, Emanuele Giuseppe Esposito wrote:
> This requires changing all vmcb_is_intercept(&svm->nested.ctl, ...)
> calls with vmcb12_is_intercept().
>
> In addition, in svm_get_nested_state() user space expects a
> vmcb_control_area struct, so we need to copy back all fields
> in a temporary structure to provide to the user space.
>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
> arch/x86/kvm/svm/nested.c | 41 +++++++++++++++++++++++----------------
> arch/x86/kvm/svm/svm.c | 4 ++--
> arch/x86/kvm/svm/svm.h | 8 ++++----
> 3 files changed, 30 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index c84cded1dcf6..13be1002ad1c 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -58,8 +58,9 @@ static void svm_inject_page_fault_nested(struct kvm_vcpu *vcpu, struct x86_excep
> struct vcpu_svm *svm = to_svm(vcpu);
> WARN_ON(!is_guest_mode(vcpu));
>
> - if (vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_EXCEPTION_OFFSET + PF_VECTOR) &&
> - !svm->nested.nested_run_pending) {
> + if (vmcb12_is_intercept(&svm->nested.ctl,
> + INTERCEPT_EXCEPTION_OFFSET + PF_VECTOR) &&
> + !svm->nested.nested_run_pending) {
> svm->vmcb->control.exit_code = SVM_EXIT_EXCP_BASE + PF_VECTOR;
> svm->vmcb->control.exit_code_hi = 0;
> svm->vmcb->control.exit_info_1 = fault->error_code;
> @@ -121,7 +122,8 @@ static void nested_svm_uninit_mmu_context(struct kvm_vcpu *vcpu)
>
> void recalc_intercepts(struct vcpu_svm *svm)
> {
> - struct vmcb_control_area *c, *h, *g;
> + struct vmcb_control_area *c, *h;
> + struct vmcb_ctrl_area_cached *g;
> unsigned int i;
>
> vmcb_mark_dirty(svm->vmcb, VMCB_INTERCEPTS);
> @@ -172,7 +174,7 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
> */
> int i;
>
> - if (!(vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
> + if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
> return true;
>
> for (i = 0; i < MSRPM_OFFSETS; i++) {
> @@ -208,9 +210,9 @@ static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa, u32 size)
> }
>
> static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
> - struct vmcb_control_area *control)
> + struct vmcb_ctrl_area_cached *control)
> {
> - if (CC(!vmcb_is_intercept(control, INTERCEPT_VMRUN)))
> + if (CC(!vmcb12_is_intercept(control, INTERCEPT_VMRUN)))
> return false;
>
> if (CC(control->asid == 0))
> @@ -960,7 +962,7 @@ static int nested_svm_exit_handled_msr(struct vcpu_svm *svm)
> u32 offset, msr, value;
> int write, mask;
>
> - if (!(vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
> + if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
> return NESTED_EXIT_HOST;
>
> msr = svm->vcpu.arch.regs[VCPU_REGS_RCX];
> @@ -987,7 +989,7 @@ static int nested_svm_intercept_ioio(struct vcpu_svm *svm)
> u8 start_bit;
> u64 gpa;
>
> - if (!(vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_IOIO_PROT)))
> + if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_IOIO_PROT)))
> return NESTED_EXIT_HOST;
>
> port = svm->vmcb->control.exit_info_1 >> 16;
> @@ -1018,12 +1020,12 @@ static int nested_svm_intercept(struct vcpu_svm *svm)
> vmexit = nested_svm_intercept_ioio(svm);
> break;
> case SVM_EXIT_READ_CR0 ... SVM_EXIT_WRITE_CR8: {
> - if (vmcb_is_intercept(&svm->nested.ctl, exit_code))
> + if (vmcb12_is_intercept(&svm->nested.ctl, exit_code))
> vmexit = NESTED_EXIT_DONE;
> break;
> }
> case SVM_EXIT_READ_DR0 ... SVM_EXIT_WRITE_DR7: {
> - if (vmcb_is_intercept(&svm->nested.ctl, exit_code))
> + if (vmcb12_is_intercept(&svm->nested.ctl, exit_code))
> vmexit = NESTED_EXIT_DONE;
> break;
> }
> @@ -1041,7 +1043,7 @@ static int nested_svm_intercept(struct vcpu_svm *svm)
> break;
> }
> default: {
> - if (vmcb_is_intercept(&svm->nested.ctl, exit_code))
> + if (vmcb12_is_intercept(&svm->nested.ctl, exit_code))
> vmexit = NESTED_EXIT_DONE;
> }
> }
> @@ -1119,7 +1121,7 @@ static void nested_svm_inject_exception_vmexit(struct vcpu_svm *svm)
>
> static inline bool nested_exit_on_init(struct vcpu_svm *svm)
> {
> - return vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_INIT);
> + return vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_INIT);
> }
>
> static int svm_check_nested_events(struct kvm_vcpu *vcpu)
> @@ -1250,6 +1252,7 @@ static int svm_get_nested_state(struct kvm_vcpu *vcpu,
> u32 user_data_size)
> {
> struct vcpu_svm *svm;
> + struct vmcb_control_area ctl_temp;
> struct kvm_nested_state kvm_state = {
> .flags = 0,
> .format = KVM_STATE_NESTED_FORMAT_SVM,
> @@ -1291,7 +1294,8 @@ static int svm_get_nested_state(struct kvm_vcpu *vcpu,
> */
> if (clear_user(user_vmcb, KVM_STATE_NESTED_SVM_VMCB_SIZE))
> return -EFAULT;
> - if (copy_to_user(&user_vmcb->control, &svm->nested.ctl,
> + nested_copy_vmcb_cache_to_control(&ctl_temp, &svm->nested.ctl);
> + if (copy_to_user(&user_vmcb->control, &ctl_temp,
> sizeof(user_vmcb->control)))
> return -EFAULT;
> if (copy_to_user(&user_vmcb->save, &svm->vmcb01.ptr->save,
> @@ -1362,8 +1366,9 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> goto out_free;
>
> ret = -EINVAL;
> - if (!nested_vmcb_check_controls(vcpu, ctl))
> - goto out_free;
> + nested_copy_vmcb_control_to_cache(svm, ctl);
> + if (!nested_vmcb_check_controls(vcpu, &svm->nested.ctl))
> + goto out_free_ctl;

I also don't like this, like about writing and clearing of svm->nested.save in patch 4.
Unlike the former case, this case is functionally correct, but still a failure will
leave partially initialized state (which you zero at the end to make it better, but it is best
that failure would leave the state untouched).

Since loading/saving the nested state is anything but performance critical code,
I would prefer to also copy control area to a temp variable, and then pass it to
__nested_vmcb_check_controls.

Other than that, this patch looks good.

Best regards,
Maxim Levitsky

>
> /*
> * Processor state contains L2 state. Check that it is
> @@ -1371,7 +1376,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> */
> cr0 = kvm_read_cr0(vcpu);
> if (((cr0 & X86_CR0_CD) == 0) && (cr0 & X86_CR0_NW))
> - goto out_free;
> + goto out_free_ctl;
>
> /*
> * Validate host state saved from before VMRUN (see
> @@ -1417,7 +1422,6 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> svm->nested.vmcb12_gpa = kvm_state->hdr.svm.vmcb_pa;
>
> svm_copy_vmrun_state(&svm->vmcb01.ptr->save, save);
> - nested_copy_vmcb_control_to_cache(svm, ctl);
>
> svm_switch_vmcb(svm, &svm->nested.vmcb02);
> nested_vmcb02_prepare_control(svm);
> @@ -1427,6 +1431,9 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> out_free_save:
> memset(&svm->nested.save, 0, sizeof(struct vmcb_save_area_cached));
>
> +out_free_ctl:
> + memset(&svm->nested.ctl, 0, sizeof(struct vmcb_ctrl_area_cached));
> +
> out_free:
> kfree(save);
> kfree(ctl);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 1b6d25c6e0ae..d866eea39777 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2465,7 +2465,7 @@ static bool check_selective_cr0_intercepted(struct kvm_vcpu *vcpu,
> bool ret = false;
>
> if (!is_guest_mode(vcpu) ||
> - (!(vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_SELECTIVE_CR0))))
> + (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_SELECTIVE_CR0))))
> return false;
>
> cr0 &= ~SVM_CR0_SELECTIVE_MASK;
> @@ -4184,7 +4184,7 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
> info->intercept == x86_intercept_clts)
> break;
>
> - if (!(vmcb_is_intercept(&svm->nested.ctl,
> + if (!(vmcb12_is_intercept(&svm->nested.ctl,
> INTERCEPT_SELECTIVE_CR0)))
> break;
>
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 78006245e334..051b7d0a13a1 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -156,7 +156,7 @@ struct svm_nested_state {
> bool nested_run_pending;
>
> /* cache for control fields of the guest */
> - struct vmcb_control_area ctl;
> + struct vmcb_ctrl_area_cached ctl;
> struct vmcb_save_area_cached save;
>
> bool initialized;
> @@ -491,17 +491,17 @@ static inline bool nested_svm_virtualize_tpr(struct kvm_vcpu *vcpu)
>
> static inline bool nested_exit_on_smi(struct vcpu_svm *svm)
> {
> - return vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_SMI);
> + return vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_SMI);
> }
>
> static inline bool nested_exit_on_intr(struct vcpu_svm *svm)
> {
> - return vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_INTR);
> + return vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_INTR);
> }
>
> static inline bool nested_exit_on_nmi(struct vcpu_svm *svm)
> {
> - return vmcb_is_intercept(&svm->nested.ctl, INTERCEPT_NMI);
> + return vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_NMI);
> }
>
> int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb_gpa, struct vmcb *vmcb12);