Re: [PATCH v3 8/9] target/i386: SEV: Add support for setting TSC frequency for Secure TSC

[Markus Armbruster <armbru@redhat.com>]

Pardon my ignorance...

"Naveen N Rao (AMD)" <naveen@kernel.org> writes:

> Add support for configuring the TSC frequency when Secure TSC is enabled
> in SEV-SNP guests through a new "tsc-frequency" property on SEV-SNP
> guest objects, similar to the vCPU-specific property used by regular
> guests and TDX.

Which property exactly?

>                 A new property is needed since SEV-SNP guests require
> the TSC frequency to be specified during early SNP_LAUNCH_START command
> before any vCPUs are created.

Sounds awkward.

Do the two properties set the same thing at different times?

> The user-provided TSC frequency is set through KVM_SET_TSC_KHZ before
> issuing KVM_SEV_SNP_LAUNCH_START.
>
> Attempts to set TSC frequency on both the SEV_SNP object and the cpu
> object result in an error from KVM (on the vCPU ioctl), so do not add
> separate checks for the same.
>
> Sample command-line:
>   -machine q35,confidential-guest-support=sev0 \
>   -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1,secure-tsc=on,tsc-frequency=2500000000
>
> Co-developed-by: Ketan Chaturvedi <Ketan.Chaturvedi@amd.com>
> Signed-off-by: Ketan Chaturvedi <Ketan.Chaturvedi@amd.com>
> Co-developed-by: Nikunj A Dadhania <nikunj@amd.com>
> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
> Signed-off-by: Naveen N Rao (AMD) <naveen@kernel.org>

[...]

> diff --git a/qapi/qom.json b/qapi/qom.json
> index c7dd2dd1b095..5daaf065b6b7 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -1104,6 +1104,9 @@
>  # @secure-tsc: enable Secure TSC
>  #     (default: false) (since 10.2)
>  #
> +# @tsc-frequency: set secure TSC frequency.  Only valid if Secure TSC
> +#     is enabled (default: zero) (since 10.2)

Is this likely to remain the only property that's only valied when
@secure-tsc is true?

> +#
>  # Since: 9.1
>  ##
>  { 'struct': 'SevSnpGuestProperties',
> @@ -1116,7 +1119,8 @@
>              '*author-key-enabled': 'bool',
>              '*host-data': 'str',
>              '*vcek-disabled': 'bool',
> -            '*secure-tsc': 'bool' } }
> +            '*secure-tsc': 'bool',
> +            '*tsc-frequency': 'uint32' } }
>  
>  ##
>  # @TdxGuestProperties: