On Fri, Apr 17, 2020 at 11:34:51AM -0700, Makarand Sonare wrote:
> From: Peter Shier <pshier@xxxxxxxxxx>
>
> Add new field to hold preemption timer remaining until expiration
> appended to struct kvm_vmx_nested_state_data. KVM_SET_NESTED_STATE restarts
> timer using migrated state regardless of whether L1 sets
> VM_EXIT_SAVE_VMX_PREEMPTION_TIMER.
The changelog should call out that simply stuffing vmcs12 will cause
incorrect behavior because the second (and later) VM-Enter after migration
will restart the timer with the wrong value. It took me a bit to piece
together why the extra field was needed.
> -static void vmx_start_preemption_timer(struct kvm_vcpu *vcpu)
> +static void vmx_start_preemption_timer(struct kvm_vcpu *vcpu,
> + u64 preemption_timeout)
> {
> - u64 preemption_timeout = get_vmcs12(vcpu)->vmx_preemption_timer_value;
> struct vcpu_vmx *vmx = to_vmx(vcpu);
>
> /*
> @@ -3293,8 +3294,15 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
> * the timer.
> */
> vmx->nested.preemption_timer_expired = false;
> - if (nested_cpu_has_preemption_timer(vmcs12))
> - vmx_start_preemption_timer(vcpu);
> + if (nested_cpu_has_preemption_timer(vmcs12)) {
> + u64 preemption_timeout;
timer_value would be shorter, and IMO, a better name as well. I'd even go
so far as to say throw on a follow-up patch to rename the variable in
vmx_start_preemption_timer.
> + if (from_vmentry)
> + preemption_timeout = get_vmcs12(vcpu)->vmx_preemption_timer_value;
vmcs12 is already available.
> + else
> + preemption_timeout = vmx->nested.preemption_timer_remaining;
> + vmx_start_preemption_timer(vcpu, preemption_timeout);
> + }
>
> /*
> * Note no nested_vmx_succeed or nested_vmx_fail here. At this point
> @@ -3888,10 +3896,13 @@ static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
> else
> vmcs12->guest_activity_state = GUEST_ACTIVITY_ACTIVE;
>
> - if (nested_cpu_has_preemption_timer(vmcs12) &&
> - vmcs12->vm_exit_controls & VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)
> + if (nested_cpu_has_preemption_timer(vmcs12)) {
> + vmx->nested.preemption_timer_remaining =
> + vmx_get_preemption_timer_value(vcpu);
> + if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)
> vmcs12->vmx_preemption_timer_value =
> - vmx_get_preemption_timer_value(vcpu);
> + vmx->nested.preemption_timer_remaining;
> + }
>
> /*
> * In some cases (usually, nested EPT), L2 is allowed to change its
> @@ -5759,6 +5770,13 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
>
> if (vmx->nested.mtf_pending)
> kvm_state.flags |= KVM_STATE_NESTED_MTF_PENDING;
> +
> + if (nested_cpu_has_preemption_timer(vmcs12)) {
> + kvm_state.flags |=
> + KVM_STATE_NESTED_PREEMPTION_TIMER;
> + kvm_state.size +=
> + sizeof(user_vmx_nested_state->preemption_timer_remaining);
> + }
> }
> }
>
> @@ -5790,6 +5808,9 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
>
> BUILD_BUG_ON(sizeof(user_vmx_nested_state->vmcs12) < VMCS12_SIZE);
> BUILD_BUG_ON(sizeof(user_vmx_nested_state->shadow_vmcs12) < VMCS12_SIZE);
> + BUILD_BUG_ON(sizeof(user_vmx_nested_state->preemption_timer_remaining)
> + != sizeof(vmx->nested.preemption_timer_remaining));
> +
>
> /*
> * Copy over the full allocated size of vmcs12 rather than just the size
> @@ -5805,6 +5826,13 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
> return -EFAULT;
> }
>
> + if (kvm_state.flags & KVM_STATE_NESTED_PREEMPTION_TIMER) {
> + if (copy_to_user(&user_vmx_nested_state->preemption_timer_remaining,
> + &vmx->nested.preemption_timer_remaining,
> + sizeof(vmx->nested.preemption_timer_remaining)))
> + return -EFAULT;
Isn't this suitable for put_user()? That would allow dropping the
long-winded BUILD_BUG_ON.
> + }
> +
> out:
> return kvm_state.size;
> }
> @@ -5876,7 +5904,8 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
> */
> if (is_smm(vcpu) ?
> (kvm_state->flags &
> - (KVM_STATE_NESTED_GUEST_MODE | KVM_STATE_NESTED_RUN_PENDING))
> + (KVM_STATE_NESTED_GUEST_MODE | KVM_STATE_NESTED_RUN_PENDING |
> + KVM_STATE_NESTED_PREEMPTION_TIMER))
> : kvm_state->hdr.vmx.smm.flags)
> return -EINVAL;
>
> @@ -5966,6 +5995,23 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
> goto error_guest_mode;
> }
>
> + if (kvm_state->flags & KVM_STATE_NESTED_PREEMPTION_TIMER) {
> +
> + if (kvm_state->size <
> + sizeof(*kvm_state) +
> + sizeof(user_vmx_nested_state->vmcs12) +
> + sizeof(user_vmx_nested_state->shadow_vmcs12) +
> + sizeof(user_vmx_nested_state->preemption_timer_remaining))
if (kvm_state->size <
offsetof(struct kvm_nested_state, vmx) +
offsetofend(struct kvm_nested_state_data,
preemption_timer_remaining))
> + goto error_guest_mode;
> +
> + if (copy_from_user(&vmx->nested.preemption_timer_remaining,
> + &user_vmx_nested_state->preemption_timer_remaining,
> + sizeof(user_vmx_nested_state->preemption_timer_remaining))) {
> + ret = -EFAULT;
> + goto error_guest_mode;
> + }
> + }
> +
> if (nested_vmx_check_controls(vcpu, vmcs12) ||
> nested_vmx_check_host_state(vcpu, vmcs12) ||
> nested_vmx_check_guest_state(vcpu, vmcs12, &exit_qual))
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index aab9df55336ef..0098c7dc2e254 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -167,6 +167,7 @@ struct nested_vmx {
> u16 posted_intr_nv;
>
> struct hrtimer preemption_timer;
> + u32 preemption_timer_remaining;
> bool preemption_timer_expired;
>
> /* to migrate it to L2 if VM_ENTRY_LOAD_DEBUG_CONTROLS is off */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 027dfd278a973..ddad6305a0d23 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3374,6 +3374,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_GET_MSR_FEATURES:
> case KVM_CAP_MSR_PLATFORM_INFO:
> case KVM_CAP_EXCEPTION_PAYLOAD:
> + case KVM_CAP_NESTED_PREEMPTION_TIMER:
Maybe KVM_CAP_NESTED_STATE_PREEMPTION_TIMER?
> r = 1;
> break;
> case KVM_CAP_SYNC_REGS:
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 428c7dde6b4b3..489c3df0b49c8 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1017,6 +1017,7 @@ struct kvm_ppc_resize_hpt {
> #define KVM_CAP_S390_VCPU_RESETS 179
> #define KVM_CAP_S390_PROTECTED 180
> #define KVM_CAP_PPC_SECURE_GUEST 181
> +#define KVM_CAP_NESTED_PREEMPTION_TIMER 182
>
> #ifdef KVM_CAP_IRQ_ROUTING
>
> diff --git a/tools/arch/x86/include/uapi/asm/kvm.h b/tools/arch/x86/include/uapi/asm/kvm.h
> index 3f3f780c8c650..ac8e5d391356c 100644
> --- a/tools/arch/x86/include/uapi/asm/kvm.h
> +++ b/tools/arch/x86/include/uapi/asm/kvm.h
> @@ -391,6 +391,8 @@ struct kvm_sync_regs {
> #define KVM_STATE_NESTED_RUN_PENDING 0x00000002
> #define KVM_STATE_NESTED_EVMCS 0x00000004
> #define KVM_STATE_NESTED_MTF_PENDING 0x00000008
> +/* Available with KVM_CAP_NESTED_PREEMPTION_TIMER */
> +#define KVM_STATE_NESTED_PREEMPTION_TIMER 0x00000010
>
> #define KVM_STATE_NESTED_SMM_GUEST_MODE 0x00000001
> #define KVM_STATE_NESTED_SMM_VMXON 0x00000002
> --
> 2.26.1.301.g55bc3eb7cb9-goog
>
