Re: [PATCH v6 13/13] s390: Recognize confidential-guest-support option

[Christian Borntraeger]

On 12.01.21 05:45, David Gibson wrote:
> At least some s390 cpu models support "Protected Virtualization" (PV),
> a mechanism to protect guests from eavesdropping by a compromised
> hypervisor.
> 
> This is similar in function to other mechanisms like AMD's SEV and
> POWER's PEF, which are controlled by the "confidential-guest-support"
> machine option.  s390 is a slightly special case, because we already
> supported PV, simply by using a CPU model with the required feature
> (S390_FEAT_UNPACK).
> 
> To integrate this with the option used by other platforms, we
> implement the following compromise:
> 
>  - When the confidential-guest-support option is set, s390 will
>    recognize it, verify that the CPU can support PV (failing if not)
>    and set virtio default options necessary for encrypted or protected
>    guests, as on other platforms.  i.e. if confidential-guest-support
>    is set, we will either create a guest capable of entering PV mode,
>    or fail outright.
> 
>  - If confidential-guest-support is not set, guests might still be
>    able to enter PV mode, if the CPU has the right model.  This may be
>    a little surprising, but shouldn't actually be harmful.
> 
> To start a guest supporting Protected Virtualization using the new
> option use the command line arguments:
>     -object s390-pv-guest,id=pv0 -machine confidential-guest-support=pv0


This results in

[cborntra@t35lp61 qemu]$ qemu-system-s390x -enable-kvm -nographic -m 2G -kernel 
~/full.normal 
**
ERROR:../qom/object.c:317:type_initialize: assertion failed: 
(parent->instance_size <= ti->instance_size)
Bail out! ERROR:../qom/object.c:317:type_initialize: assertion failed: 
(parent->instance_size <= ti->instance_size)
Aborted (core dumped)




> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  docs/confidential-guest-support.txt |  3 ++
>  docs/system/s390x/protvirt.rst      | 19 +++++++---
>  hw/s390x/pv.c                       | 58 +++++++++++++++++++++++++++++
>  include/hw/s390x/pv.h               |  1 +
>  target/s390x/kvm.c                  |  3 ++
>  5 files changed, 78 insertions(+), 6 deletions(-)
> 
> diff --git a/docs/confidential-guest-support.txt 
> b/docs/confidential-guest-support.txt
> index d466aa79d5..b4912f66c2 100644
> --- a/docs/confidential-guest-support.txt
> +++ b/docs/confidential-guest-support.txt
> @@ -42,4 +42,7 @@ AMD Secure Encrypted Virtualization (SEV)
>  
>  POWER Protected Execution Facility (PEF)
>  
> +s390x Protected Virtualization (PV)
> +    docs/system/s390x/protvirt.rst
> +
>  Other mechanisms may be supported in future.
> diff --git a/docs/system/s390x/protvirt.rst b/docs/system/s390x/protvirt.rst
> index 712974ad87..0f481043d9 100644
> --- a/docs/system/s390x/protvirt.rst
> +++ b/docs/system/s390x/protvirt.rst
> @@ -22,15 +22,22 @@ If those requirements are met, the capability 
> `KVM_CAP_S390_PROTECTED`
>  will indicate that KVM can support PVMs on that LPAR.
>  
>  
> -QEMU Settings
> --------------
> +Running a Protected Virtual Machine
> +-----------------------------------
>  
> -To indicate to the VM that it can transition into protected mode, the
> +To run a PVM you will need to select a CPU model which includes the
>  `Unpack facility` (stfle bit 161 represented by the feature
> -`unpack`/`S390_FEAT_UNPACK`) needs to be part of the cpu model of
> -the VM.
> +`unpack`/`S390_FEAT_UNPACK`), and add these options to the command line::
> +
> +    -object s390-pv-guest,id=pv0 \
> +    -machine confidential-guest-support=pv0
> +
> +Adding these options will:
> +
> +* Ensure the `unpack` facility is available
> +* Enable the IOMMU by default for all I/O devices
> +* Initialize the PV mechanism
>  
> -All I/O devices need to use the IOMMU.
>  Passthrough (vfio) devices are currently not supported.
>  
>  Host huge page backings are not supported. However guests can use huge
> diff --git a/hw/s390x/pv.c b/hw/s390x/pv.c
> index ab3a2482aa..85592e100a 100644
> --- a/hw/s390x/pv.c
> +++ b/hw/s390x/pv.c
> @@ -14,8 +14,11 @@
>  #include <linux/kvm.h>
>  
>  #include "cpu.h"
> +#include "qapi/error.h"
>  #include "qemu/error-report.h"
>  #include "sysemu/kvm.h"
> +#include "qom/object_interfaces.h"
> +#include "exec/confidential-guest-support.h"
>  #include "hw/s390x/ipl.h"
>  #include "hw/s390x/pv.h"
>  
> @@ -111,3 +114,58 @@ void s390_pv_inject_reset_error(CPUState *cs)
>      /* Report that we are unable to enter protected mode */
>      env->regs[r1 + 1] = DIAG_308_RC_INVAL_FOR_PV;
>  }
> +
> +#define TYPE_S390_PV_GUEST "s390-pv-guest"
> +#define S390_PV_GUEST(obj)                              \
> +    OBJECT_CHECK(S390PVGuestState, (obj), TYPE_S390_PV_GUEST)
> +
> +typedef struct S390PVGuestState S390PVGuestState;
> +
> +/**
> + * S390PVGuestState:
> + *
> + * The S390PVGuestState object is basically a dummy used to tell the
> + * confidential guest support system to use s390's PV mechanism.
> + *
> + * # $QEMU \
> + *         -object s390-pv-guest,id=pv0 \
> + *         -machine ...,confidential-guest-support=pv0
> + */
> +struct S390PVGuestState {
> +    Object parent_obj;
> +};
> +
> +int s390_pv_init(ConfidentialGuestSupport *cgs, Error **errp)
> +{
> +    if (!object_dynamic_cast(OBJECT(cgs), TYPE_S390_PV_GUEST)) {
> +        return 0;
> +    }
> +
> +    if (!s390_has_feat(S390_FEAT_UNPACK)) {
> +        error_setg(errp,
> +                   "CPU model does not support Protected Virtualization");
> +        return -1;
> +    }
> +
> +    cgs->ready = true;
> +
> +    return 0;
> +}
> +
> +static const TypeInfo s390_pv_guest_info = {
> +    .parent = TYPE_CONFIDENTIAL_GUEST_SUPPORT,
> +    .name = TYPE_S390_PV_GUEST,
> +    .instance_size = sizeof(S390PVGuestState),
> +    .interfaces = (InterfaceInfo[]) {
> +        { TYPE_USER_CREATABLE },
> +        { }
> +    }
> +};
> +
> +static void
> +s390_pv_register_types(void)
> +{
> +    type_register_static(&s390_pv_guest_info);
> +}
> +
> +type_init(s390_pv_register_types);
> diff --git a/include/hw/s390x/pv.h b/include/hw/s390x/pv.h
> index aee758bc2d..9bbf66f356 100644
> --- a/include/hw/s390x/pv.h
> +++ b/include/hw/s390x/pv.h
> @@ -43,6 +43,7 @@ void s390_pv_prep_reset(void);
>  int s390_pv_verify(void);
>  void s390_pv_unshare(void);
>  void s390_pv_inject_reset_error(CPUState *cs);
> +int s390_pv_init(ConfidentialGuestSupport *cgs, Error **errp);
>  #else /* CONFIG_KVM */
>  static inline bool s390_is_pv(void) { return false; }
>  static inline int s390_pv_vm_enable(void) { return 0; }
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index b8385e6b95..d2435664dc 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -387,6 +387,9 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>      }
>  
>      kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES);
> +
> +    s390_pv_init(ms->cgs, &error_fatal);
> +
>      return 0;
>  }
>  
>