Re: [Qemu-devel] [PATCH v2] target/i386: sev: add 'sev-max-guests' field to 'query-sev-capabilities'

[Erik Skultety <eskultet@redhat.com>]

On Thu, Apr 11, 2019 at 11:55:15PM +0000, Singh, Brijesh wrote:
> There are limited numbers of the SEV guests that can be run concurrently.
> A management applications may need to know this limit so that it can place
> SEV VMs on hosts which have suitable resources available.
>
> Currently, this limit is not exposed to the application. Add a new
> 'sev-max-guest' field in the query-sev-capabilities to provide this
> information.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Markus Armbruster <armbru@redhat.com>
> Cc: Eric Blake <eblake@redhat.com>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Erik Skultety <eskultet@redhat.com>
> Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>
> changes since v1:
>  - document the new field and add (since 4.1) annotation.
>
>  qapi/target.json  | 9 +++++++--
>  target/i386/sev.c | 9 +++++++--
>  2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/qapi/target.json b/qapi/target.json
> index 1d4d54b600..8cd4fc7919 100644
> --- a/qapi/target.json
> +++ b/qapi/target.json
> @@ -177,13 +177,17 @@
>  # @reduced-phys-bits: Number of physical Address bit reduction when SEV is
>  #                     enabled
>  #
> +# @sev-max-guests: maximum number of concurrent SEV guest with SEV-ES disabled
> +#                  (since 4.1)
> +#
>  # Since: 2.12
>  ##
>  { 'struct': 'SevCapability',
>    'data': { 'pdh': 'str',
>              'cert-chain': 'str',
>              'cbitpos': 'int',
> -            'reduced-phys-bits': 'int'},
> +            'reduced-phys-bits': 'int',
> +            'sev-max-guests': 'int'},
>    'if': 'defined(TARGET_I386)' }
>
>  ##
> @@ -200,7 +204,8 @@
>  #
>  # -> { "execute": "query-sev-capabilities" }
>  # <- { "return": { "pdh": "8CCDD8DDD", "cert-chain": "888CCCDDDEE",
> -#                  "cbitpos": 47, "reduced-phys-bits": 5}}
> +#                  "cbitpos": 47, "reduced-phys-bits": 5,
> +#                  "sev-max-guests" : 15}}
>  #
>  ##
>  { 'command': 'query-sev-capabilities', 'returns': 'SevCapability',
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index cd77f6b5d4..6829586fbe 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -488,7 +488,7 @@ sev_get_capabilities(void)
>      guchar *pdh_data = NULL;
>      guchar *cert_chain_data = NULL;
>      size_t pdh_len = 0, cert_chain_len = 0;
> -    uint32_t ebx;
> +    uint32_t ebx, ecx, edx;
>      int fd;
>
>      fd = open(DEFAULT_SEV_DEVICE, O_RDWR);
> @@ -507,7 +507,7 @@ sev_get_capabilities(void)
>      cap->pdh = g_base64_encode(pdh_data, pdh_len);
>      cap->cert_chain = g_base64_encode(cert_chain_data, cert_chain_len);
>
> -    host_cpuid(0x8000001F, 0, NULL, &ebx, NULL, NULL);
> +    host_cpuid(0x8000001F, 0, NULL, &ebx, &ecx, &edx);
>      cap->cbitpos = ebx & 0x3f;
>
>      /*
> @@ -516,6 +516,11 @@ sev_get_capabilities(void)
>       */
>      cap->reduced_phys_bits = 1;
>
> +    /*
> +     * The maximum number of SEV guests with SEV-ES disabled that can run
> +     * simultaneously.
> +     */
> +    cap->sev_max_guests = ecx - edx + 1;

I'm not that familiar with QEMU code, so I guess ^this works as intended, but
to the idea (and per my comment in v1):

Reviewed-by: Erik Skultety <eskultet@redhat.com>