Re: [RFC PATCH v2 12/12] i386/sev: update query-sev QAPI format to handle SEV-SNP

[Markus Armbruster <armbru@redhat.com>]

Michael Roth <michael.roth@amd.com> writes:

> Most of the current 'query-sev' command is relevant to both legacy
> SEV/SEV-ES guests and SEV-SNP guests, with 2 exceptions:
>
>   - 'policy' is a 64-bit field for SEV-SNP, not 32-bit, and
>     the meaning of the bit positions has changed
>   - 'handle' is not relevant to SEV-SNP
>
> To address this, this patch adds a new 'sev-type' field that can be
> used as a discriminator to select between SEV and SEV-SNP-specific
> fields/formats without breaking compatibility for existing management
> tools (so long as management tools that add support for launching
> SEV-SNP guest update their handling of query-sev appropriately).

Technically a compatibility break: query-sev can now return an object
that whose member @policy has different meaning, and also lacks @handle.

Matrix:

                            Old mgmt app    New mgmt app
    Old QEMU, SEV/SEV-ES       good            good(1)
    New QEMU, SEV/SEV-ES       good(2)         good
    New QEMU, SEV-SNP           bad(3)         good

Notes:

(1) As long as the management application can cope with absent member
@sev-type.

(2) As long as the management application ignores unknown member
@sev-type.

(3) Management application may choke on missing member @handle, or
worse, misinterpret member @policy.  Can only happen when something
other than the management application created the SEV-SNP guest (or the
user somehow made the management application create one even though it
doesn't know how, say with CLI option passthrough, but that's always
fragile, and I wouldn't worry about it here).

I think (1) and (2) are reasonable.  (3) is an issue for management
applications that support attaching to existing guests.  Thoughts?

>
> The corresponding HMP command has also been fixed up similarly.
>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---
>  qapi/misc-target.json  | 71 +++++++++++++++++++++++++++++++++---------
>  target/i386/monitor.c  | 29 +++++++++++++----
>  target/i386/sev.c      | 22 +++++++------
>  target/i386/sev_i386.h |  3 ++
>  4 files changed, 95 insertions(+), 30 deletions(-)
>
> diff --git a/qapi/misc-target.json b/qapi/misc-target.json
> index 3b05ad3dbf..80f994ff9b 100644
> --- a/qapi/misc-target.json
> +++ b/qapi/misc-target.json
> @@ -81,6 +81,49 @@
>             'send-update', 'receive-update' ],
>    'if': 'TARGET_I386' }
>  
> +##
> +# @SevGuestType:
> +#
> +# An enumeration indicating the type of SEV guest being run.
> +#
> +# @sev:     The guest is a legacy SEV or SEV-ES guest.
> +# @sev-snp: The guest is an SEV-SNP guest.
> +#
> +# Since: 6.2
> +##
> +{ 'enum': 'SevGuestType',
> +  'data': [ 'sev', 'sev-snp' ],
> +  'if': 'TARGET_I386' }
> +
> +##
> +# @SevGuestInfo:
> +#
> +# Information specific to legacy SEV/SEV-ES guests.
> +#
> +# @policy: SEV policy value
> +#
> +# @handle: SEV firmware handle
> +#
> +# Since: 2.12
> +##
> +{ 'struct': 'SevGuestInfo',
> +  'data': { 'policy': 'uint32',
> +            'handle': 'uint32' },
> +  'if': 'TARGET_I386' }
> +
> +##
> +# @SevSnpGuestInfo:
> +#
> +# Information specific to SEV-SNP guests.
> +#
> +# @policy: SEV-SNP policy value
> +#
> +# Since: 6.2
> +##
> +{ 'struct': 'SevSnpGuestInfo',
> +  'data': { 'policy': 'uint64' },
> +  'if': 'TARGET_I386' }
> +
>  ##
>  # @SevInfo:
>  #
> @@ -94,25 +137,25 @@
>  #
>  # @build-id: SEV FW build id
>  #
> -# @policy: SEV policy value
> -#
>  # @state: SEV guest state
>  #
> -# @handle: SEV firmware handle
> +# @sev-type: Type of SEV guest being run
>  #
>  # Since: 2.12
>  ##
> -{ 'struct': 'SevInfo',
> -    'data': { 'enabled': 'bool',
> -              'api-major': 'uint8',
> -              'api-minor' : 'uint8',
> -              'build-id' : 'uint8',
> -              'policy' : 'uint32',
> -              'state' : 'SevState',
> -              'handle' : 'uint32'
> -            },
> -  'if': 'TARGET_I386'
> -}
> +{ 'union': 'SevInfo',
> +  'base': { 'enabled': 'bool',
> +            'api-major': 'uint8',
> +            'api-minor' : 'uint8',
> +            'build-id' : 'uint8',
> +            'state' : 'SevState',
> +            'sev-type' : 'SevGuestType' },
> +  'discriminator': 'sev-type',
> +  'data': {
> +      'sev': 'SevGuestInfo',
> +      'sev-snp': 'SevSnpGuestInfo' },
> +  'if': 'TARGET_I386' }
> +
>  
>  ##
>  # @query-sev:

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