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SubjectRe: [PATCH v5 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor
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> +static inline bool nested_cpu_has_eptp_switching(struct vmcs12 *vmcs12)
> +{
> + return nested_cpu_has_vmfunc(vmcs12) &&
> + (vmcs12->vm_function_control &
> + VMX_VMFUNC_EPTP_SWITCHING);
> +}
> +
> static inline bool is_nmi(u32 intr_info)
> {
> return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VALID_MASK))
> @@ -2791,7 +2800,12 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
> if (cpu_has_vmx_vmfunc()) {
> vmx->nested.nested_vmx_secondary_ctls_high |=
> SECONDARY_EXEC_ENABLE_VMFUNC;
> - vmx->nested.nested_vmx_vmfunc_controls = 0;
> + /*
> + * Advertise EPTP switching unconditionally
> + * since we emulate it
> + */
> + vmx->nested.nested_vmx_vmfunc_controls =
> + VMX_VMFUNC_EPTP_SWITCHING;

Should this only be advertised, if enable_ept is set (if the guest also
sees/can use SECONDARY_EXEC_ENABLE_EPT)?

> }
>
> /*
> @@ -7767,6 +7781,85 @@ static int handle_preemption_timer(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> +static bool check_ept_address_valid(struct kvm_vcpu *vcpu, u64 address)

check_..._valid -> valid_ept_address() ?

> +{
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> + u64 mask = VMX_EPT_RWX_MASK;
> + int maxphyaddr = cpuid_maxphyaddr(vcpu);
> + struct kvm_mmu *mmu = vcpu->arch.walk_mmu;
> +
> + /* Check for execute_only validity */
> + if ((address & mask) == VMX_EPT_EXECUTABLE_MASK) {
> + if (!(vmx->nested.nested_vmx_ept_caps &
> + VMX_EPT_EXECUTE_ONLY_BIT))
> + return false;
> + }
> +
> + /* Bits 5:3 must be 3 */
> + if (((address >> VMX_EPT_GAW_EPTP_SHIFT) & 0x7) != VMX_EPT_DEFAULT_GAW)
> + return false;
> +
> + /* Reserved bits should not be set */
> + if (address >> maxphyaddr || ((address >> 7) & 0x1f))
> + return false;
> +
> + /* AD, if set, should be supported */
> + if ((address & VMX_EPT_AD_ENABLE_BIT)) {
> + if (!enable_ept_ad_bits)
> + return false;
> + mmu->ept_ad = true;
> + } else
> + mmu->ept_ad = false;

I wouldn't expect a "check" function to modify the mmu. Can you move
modifying the mmu outside of this function (leaving the
enable_ept_ad_bits check in place)? (and maybe even set mmu->ept_ad
_after_ the kvm_mmu_unload(vcpu)?, just when setting vmcs12->ept_pointer?)

> +
> + return true;
> +}
> +
> +static int nested_vmx_eptp_switching(struct kvm_vcpu *vcpu,
> + struct vmcs12 *vmcs12)
> +{
> + u32 index = vcpu->arch.regs[VCPU_REGS_RCX];
> + u64 *l1_eptp_list, address;
> + struct page *page;
> +
> + if (!nested_cpu_has_eptp_switching(vmcs12) ||
> + !nested_cpu_has_ept(vmcs12))
> + return 1;
> +
> + if (index >= VMFUNC_EPTP_ENTRIES)
> + return 1;
> +
> + page = nested_get_page(vcpu, vmcs12->eptp_list_address);
> + if (!page)
> + return 1;
> +
> + l1_eptp_list = kmap(page);
> + address = l1_eptp_list[index];
> +
> + /*
> + * If the (L2) guest does a vmfunc to the currently
> + * active ept pointer, we don't have to do anything else
> + */
> + if (vmcs12->ept_pointer != address) {
> + if (!check_ept_address_valid(vcpu, address)) {
> + kunmap(page);
> + nested_release_page_clean(page);
> + return 1;
> + }
> + kvm_mmu_unload(vcpu);
> + vmcs12->ept_pointer = address;
> + /*
> + * TODO: Check what's the correct approach in case
> + * mmu reload fails. Currently, we just let the next
> + * reload potentially fail
> + */
> + kvm_mmu_reload(vcpu);

So, what actually happens if this generates a tripple fault? I guess we
will kill the (nested) hypervisor?

> + }
> +
> + kunmap(page);
> + nested_release_page_clean(page);
> + return 0;
> +}
> +
> static int handle_vmfunc(struct kvm_vcpu *vcpu)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -7786,7 +7879,16 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
> vmcs12 = get_vmcs12(vcpu);
> if ((vmcs12->vm_function_control & (1 << function)) == 0)
> goto fail;
> - WARN_ONCE(1, "VMCS12 VM function control should have been zero");
> +
> + switch (function) {
> + case 0:
> + if (nested_vmx_eptp_switching(vcpu, vmcs12))
> + goto fail;
> + break;
> + default:
> + goto fail;
> + }
> + return kvm_skip_emulated_instruction(vcpu);
>
> fail:
> nested_vmx_vmexit(vcpu, vmx->exit_reason,
> @@ -10354,10 +10456,20 @@ static int check_vmentry_prereqs(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
> vmx->nested.nested_vmx_entry_ctls_high))
> return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
>
> - if (nested_cpu_has_vmfunc(vmcs12) &&
> - (vmcs12->vm_function_control &
> - ~vmx->nested.nested_vmx_vmfunc_controls))
> - return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> + if (nested_cpu_has_vmfunc(vmcs12)) {
> + if (vmcs12->vm_function_control &
> + ~vmx->nested.nested_vmx_vmfunc_controls)
> + return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> +
> + if (nested_cpu_has_eptp_switching(vmcs12)) {
> + if (!nested_cpu_has_ept(vmcs12) ||
> + (vmcs12->eptp_list_address >>
> + cpuid_maxphyaddr(vcpu)) ||
> + !IS_ALIGNED(vmcs12->eptp_list_address, 4096))
> + return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> + }
> + }
> +
>
> if (vmcs12->cr3_target_count > nested_cpu_vmx_misc_cr3_count(vcpu))
> return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
>


--

Thanks,

David

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