Re: [Qemu-devel] [PATCH 6/7] KVM: i386: Add support for save and restore nested state

[Liran Alon]

> On 15 Jun 2019, at 3:42, Paolo Bonzini <address@hidden> wrote:
> 
> From: Liran Alon <address@hidden>
> 
> Kernel commit 8fcc4b5923af ("kvm: nVMX: Introduce KVM_CAP_NESTED_STATE")
> introduced new IOCTLs to extract and restore KVM internal state used to
> run a VM that is in VMX operation.
> 
> Utilize these IOCTLs to add support of migration of VMs which are
> running nested hypervisors.
> 
> Reviewed-by: Nikita Leshenko <address@hidden>
> Signed-off-by: Liran Alon <address@hidden>
> [Simplified subsection needed functions and computation of
> kvm_min_nested_state_len(); adjusted for upstream kernel field
> names; fixed !CONFIG_KVM compilation. - Paolo]
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
> accel/kvm/kvm-all.c   |   8 ++
> include/sysemu/kvm.h  |   1 +
> target/i386/cpu.h     |   3 +
> target/i386/kvm.c     |  52 ++++++++++++
> target/i386/machine.c | 182 ++++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 246 insertions(+)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index e4ac3386cb..e1c6c067e8 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -88,6 +88,7 @@ struct KVMState
> #ifdef KVM_CAP_SET_GUEST_DEBUG
>     QTAILQ_HEAD(, kvm_sw_breakpoint) kvm_sw_breakpoints;
> #endif
> +    uint32_t max_nested_state_len;

Note: In my next patch-series I have changed this to be “int”.

>     int many_ioeventfds;
>     int intx_set_mask;
>     bool sync_mmu;
> @@ -1677,6 +1678,8 @@ static int kvm_init(MachineState *ms)
>     s->debugregs = kvm_check_extension(s, KVM_CAP_DEBUGREGS);
> #endif
> 
> +    s->max_nested_state_len = kvm_check_extension(s, KVM_CAP_NESTED_STATE);
> +
> #ifdef KVM_CAP_IRQ_ROUTING
>     kvm_direct_msi_allowed = (kvm_check_extension(s, KVM_CAP_SIGNAL_MSI) > 0);
> #endif
> @@ -2244,6 +2247,11 @@ int kvm_has_debugregs(void)
>     return kvm_state->debugregs;
> }
> 
> +uint32_t kvm_max_nested_state_length(void)
> +{
> +    return kvm_state->max_nested_state_len;
> +}
> +
> int kvm_has_many_ioeventfds(void)
> {
>     if (!kvm_enabled()) {
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index a6d1cd190f..5eb79b594c 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -210,6 +210,7 @@ bool kvm_has_sync_mmu(void);
> int kvm_has_vcpu_events(void);
> int kvm_has_robust_singlestep(void);
> int kvm_has_debugregs(void);
> +uint32_t kvm_max_nested_state_length(void);
> int kvm_has_pit_state2(void);
> int kvm_has_many_ioeventfds(void);
> int kvm_has_gsi_routing(void);
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index bbeb7a9521..550d397807 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1355,6 +1355,9 @@ typedef struct CPUX86State {
> #if defined(CONFIG_KVM) || defined(CONFIG_HVF)
>     void *xsave_buf;
> #endif
> +#if defined(CONFIG_KVM)
> +    struct kvm_nested_state *nested_state;
> +#endif

Nice catch regarding CONFIG_KVM. Thanks for that. :)

> #if defined(CONFIG_HVF)
>     HVFX86EmulatorState *hvf_emul;
> #endif
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index dca76830ec..d48fafa22b 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -968,6 +968,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
>     struct kvm_cpuid_entry2 *c;
>     uint32_t signature[3];
>     int kvm_base = KVM_CPUID_SIGNATURE;
> +    uint32_t nested_state_len;
>     int r;
>     Error *local_err = NULL;
> 
> @@ -1368,6 +1369,13 @@ int kvm_arch_init_vcpu(CPUState *cs)
>     if (has_xsave) {
>         env->xsave_buf = qemu_memalign(4096, sizeof(struct kvm_xsave));
>     }
> +
> +    nested_state_len = kvm_max_nested_state_length();
> +    if (nested_state_len > 0) {
> +        assert(nested_state_len >= offsetof(struct kvm_nested_state, data));
> +        env->nested_state = g_malloc0(nested_state_len);

Paolo, why have you removed setting “env->nested_state->size = 
max_nested_state_len;”?

In addition, in my next patch-series I also added the following code here which 
is required:

+        if (IS_INTEL_CPU(env)) {
+            struct kvm_vmx_nested_state_hdr *vmx_hdr =
+                &env->nested_state->hdr.vmx_hdr;
+
+            vmx_hdr->vmxon_pa = -1ull;
+            vmx_hdr->vmcs12_pa = -1ull;
+        }

> +    }
> +
>     cpu->kvm_msr_buf = g_malloc0(MSR_BUF_SIZE);

Note: In my next patch-series I have also added a new kvm_arch_destroy_vcpu() 
method which is called from kvm_destroy_vcpu().
Similar to how kvm_arch_init_vcpu() is called from kvm_init_vcpu().
I use it to free both cpu->kvm_msr_buf and env->nested_state.

> 
>     if (!(env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_RDTSCP)) {
> @@ -3125,6 +3133,41 @@ static int kvm_get_debugregs(X86CPU *cpu)
>     return 0;
> }
> 
> +static int kvm_put_nested_state(X86CPU *cpu)
> +{
> +    CPUX86State *env = &cpu->env;
> +    uint32_t nested_state_len = kvm_max_nested_state_length();
> +
> +    if (nested_state_len == 0) {
> +        return 0;
> +    }
> +
> +    assert(env->nested_state->size <= nested_state_len);
> +    return kvm_vcpu_ioctl(CPU(cpu), KVM_SET_NESTED_STATE, env->nested_state);
> +}
> +
> +static int kvm_get_nested_state(X86CPU *cpu)
> +{
> +    CPUX86State *env = &cpu->env;
> +    uint32_t nested_state_len = kvm_max_nested_state_length();
> +
> +    if (nested_state_len == 0) {
> +        return 0;
> +    }
> +
> +    /*
> +     * It is possible that migration restored a smaller size into
> +     * nested_state->size than what our kernel supports.
> +     * We preserve migration origin nested_state->size for
> +     * the call to KVM_SET_NESTED_STATE but wish that our next call
> +     * to KVM_GET_NESTED_STATE will use the maximum size supported by
> +     * the kernel we're running on.
> +     */
> +    env->nested_state->size = nested_state_len;
> +
> +    return kvm_vcpu_ioctl(CPU(cpu), KVM_GET_NESTED_STATE, env->nested_state);
> +}
> +
> int kvm_arch_put_registers(CPUState *cpu, int level)
> {
>     X86CPU *x86_cpu = X86_CPU(cpu);
> @@ -3132,6 +3175,11 @@ int kvm_arch_put_registers(CPUState *cpu, int level)
> 
>     assert(cpu_is_stopped(cpu) || qemu_cpu_is_self(cpu));
> 
> +    ret = kvm_put_nested_state(x86_cpu);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
>     if (level >= KVM_PUT_RESET_STATE) {
>         ret = kvm_put_msr_feature_control(x86_cpu);
>         if (ret < 0) {
> @@ -3247,6 +3295,10 @@ int kvm_arch_get_registers(CPUState *cs)
>     if (ret < 0) {
>         goto out;
>     }
> +    ret = kvm_get_nested_state(cpu);
> +    if (ret < 0) {
> +        goto out;
> +    }
>     ret = 0;
>  out:
>     cpu_sync_bndcs_hflags(&cpu->env);
> diff --git a/target/i386/machine.c b/target/i386/machine.c
> index 41460be54b..45dbae6054 100644
> --- a/target/i386/machine.c
> +++ b/target/i386/machine.c
> @@ -246,6 +246,15 @@ static int cpu_pre_save(void *opaque)
>         env->segs[R_SS].flags &= ~(env->segs[R_SS].flags & DESC_DPL_MASK);
>     }
> 
> +#ifdef CONFIG_KVM
> +    /* Verify we have nested virtualization state from kernel if required */
> +    if (is_nested_virt_enabled(env) && !env->nested_state) {
> +        error_report("Guest enabled nested virtualization but kernel "
> +                     "do not support saving nested state");
> +        return -EINVAL;
> +    }
> +#endif
> +
>     return 0;
> }
> 
> @@ -909,6 +918,176 @@ static const VMStateDescription vmstate_tsc_khz = {
>     }
> };
> 
> +#ifdef CONFIG_KVM
> +static bool vmx_vmcs12_needed(void *opaque)
> +{
> +    struct kvm_nested_state *nested_state = opaque;
> +    return (nested_state->size > offsetof(struct kvm_nested_state,
> +                                          vmx.data[0].vmcs12));

Do you prefer this compared to checking explicitly? i.e. by:
return (nested_state->vmx.vmcs12_pa != -1ull);

> +}
> +
> +static const VMStateDescription vmstate_vmx_vmcs12_state = {
> +     .name = "cpu/kvm_nested_state/vmx/vmcs12",
> +     .version_id = 1,
> +     .minimum_version_id = 1,
> +     .needed = vmx_vmcs12_needed,
> +     .fields = (VMStateField[]) {
> +         VMSTATE_UINT8_ARRAY(vmx.data[0].vmcs12,
> +                             struct kvm_nested_state, 0x1000),
> +         VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static bool vmx_shadow_vmcs12_needed(void *opaque)
> +{
> +    struct kvm_nested_state *nested_state = opaque;
> +    return (nested_state->size > offsetof(struct kvm_nested_state,
> +                                          vmx.data[0].shadow_vmcs12));

Nice trick on how to determine if to send shadow_vmcs12 without requiring to 
check
if vmcs12 indeed have VMCS-shadowing enabled and a valid vmcs-link-ptr. :)

> +}
> +
> +static const VMStateDescription vmstate_vmx_shadow_vmcs12_state = {
> +     .name = "cpu/kvm_nested_state/vmx/shadow_vmcs12",
> +     .version_id = 1,
> +     .minimum_version_id = 1,
> +     .needed = vmx_shadow_vmcs12_needed,
> +     .fields = (VMStateField[]) {
> +         VMSTATE_UINT8_ARRAY(vmx.data[0].shadow_vmcs12,
> +                             struct kvm_nested_state, 0x1000),
> +         VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static bool vmx_nested_state_needed(void *opaque)
> +{
> +    struct kvm_nested_state *nested_state = opaque;
> +
> +    return ((nested_state->format == KVM_STATE_NESTED_FORMAT_VMX) &&
> +            (nested_state->vmx.vmxon_pa != -1ull));
> +}
> +
> +static const VMStateDescription vmstate_vmx_nested_state = {
> +     .name = "cpu/kvm_nested_state/vmx",
> +     .version_id = 1,
> +     .minimum_version_id = 1,
> +     .needed = vmx_nested_state_needed,
> +     .fields = (VMStateField[]) {
> +         VMSTATE_U64(vmx.vmxon_pa, struct kvm_nested_state),
> +         VMSTATE_U64(vmx.vmcs_pa, struct kvm_nested_state),
> +         VMSTATE_U16(vmx.smm.flags, struct kvm_nested_state),
> +         VMSTATE_END_OF_LIST()
> +    },
> +    .subsections = (const VMStateDescription*[]) {
> +        &vmstate_vmx_vmcs12_state,
> +        &vmstate_vmx_shadow_vmcs12_state,
> +        NULL,
> +    }
> +};
> +
> +static bool svm_nested_state_needed(void *opaque)
> +{
> +    struct kvm_nested_state *nested_state = opaque;
> +
> +    return (nested_state->format == KVM_STATE_NESTED_FORMAT_SVM);
> +}
> +
> +static const VMStateDescription vmstate_svm_nested_state = {
> +     .name = "cpu/kvm_nested_state/svm",
> +     .version_id = 1,
> +     .minimum_version_id = 1,
> +     .needed = svm_nested_state_needed,
> +     .fields = (VMStateField[]) {
> +         VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static bool nested_state_needed(void *opaque)
> +{
> +    X86CPU *cpu = opaque;
> +    CPUX86State *env = &cpu->env;
> +
> +    return (is_vmx_enabled(env) && 
> vmx_nested_state_needed(env->nested_state)) ||
> +           (is_svm_enabled(env) && 
> svm_nested_state_needed(env->nested_state));
> +}

As I specified in an earlier email in this patch-series, this is not entirely 
accurate.
In case vCPU is running L2 and entered SMM, then is_vmx_enabled() will return 
false because CR4 is set to 0 on entering SMM.
I consider deeming nested_state needed in case hflags specifies guest is in SMM 
mode. Any objection?

> +
> +static int nested_state_post_load(void *opaque, int version_id)
> +{
> +    X86CPU *cpu = opaque;
> +    CPUX86State *env = &cpu->env;
> +    struct kvm_nested_state *nested_state = env->nested_state;
> +    uint32_t min_nested_state_len = offsetof(struct kvm_nested_state, data);
> +    uint32_t max_nested_state_len = kvm_max_nested_state_length();
> +
> +    /*
> +     * If our kernel don't support setting nested state
> +     * and we have received nested state from migration stream,
> +     * we need to fail migration
> +     */
> +    if (max_nested_state_len == 0) {
> +        error_report("Received nested state when kernel cannot restore it");
> +        return -EINVAL;
> +    }
> +
> +    /*
> +     * Verify that the size of received nested_state struct
> +     * at least cover required header and is not larger
> +     * than the max size that our kernel support
> +     */
> +    if (nested_state->size < min_nested_state_len) {
> +        error_report("Received nested state size less than min: "
> +                     "len=%d, min=%d",
> +                     nested_state->size, min_nested_state_len);
> +        return -EINVAL;
> +    }
> +    if (nested_state->size > max_nested_state_len) {
> +        error_report("Recieved unsupported nested state size: "
> +                     "nested_state->size=%d, max=%d",
> +                     nested_state->size, max_nested_state_len);
> +        return -EINVAL;
> +    }
> +
> +    /* Verify format is valid */
> +    if ((nested_state->format != KVM_STATE_NESTED_FORMAT_VMX) &&
> +        (nested_state->format != KVM_STATE_NESTED_FORMAT_SVM)) {
> +        error_report("Received invalid nested state format: %d",
> +                     nested_state->format);
> +        return -EINVAL;
> +    }
> +
> +    return 0;
> +}
> +
> +static const VMStateDescription vmstate_kvm_nested_state = {
> +    .name = "cpu/kvm_nested_state",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_U16(flags, struct kvm_nested_state),
> +        VMSTATE_U16(format, struct kvm_nested_state),
> +        VMSTATE_U32(size, struct kvm_nested_state),
> +        VMSTATE_END_OF_LIST()
> +    },
> +    .subsections = (const VMStateDescription*[]) {
> +        &vmstate_vmx_nested_state,
> +        &vmstate_svm_nested_state,
> +        NULL
> +    }
> +};
> +
> +static const VMStateDescription vmstate_nested_state = {
> +    .name = "cpu/nested_state",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = nested_state_needed,
> +    .post_load = nested_state_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_STRUCT_POINTER(env.nested_state, X86CPU,
> +                               vmstate_kvm_nested_state,
> +                               struct kvm_nested_state),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +#endif
> +
> static bool mcg_ext_ctl_needed(void *opaque)
> {
>     X86CPU *cpu = opaque;
> @@ -1148,6 +1327,9 @@ VMStateDescription vmstate_x86_cpu = {
>         &vmstate_msr_intel_pt,
>         &vmstate_msr_virt_ssbd,
>         &vmstate_svm_npt,
> +#ifdef CONFIG_KVM
> +        &vmstate_nested_state,
> +#endif
>         NULL
>     }
> };
> -- 
> 2.21.0
> 
>