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

[Laszlo Ersek]

On 04/12/19 10:05, Paolo Bonzini wrote:
> On 12/04/19 09:58, Laszlo Ersek wrote:
>> On 04/12/19 01:55, 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 <address@hidden>
>>> Cc: Markus Armbruster <address@hidden>
>>> Cc: Eric Blake <address@hidden>
>>> Cc: Daniel P. Berrangé <address@hidden>
>>> Cc: Laszlo Ersek <address@hidden>
>>> Cc: Erik Skultety <address@hidden>
>>> Cc: Tom Lendacky <address@hidden>
>>> Signed-off-by: Brijesh Singh <address@hidden>
>>> ---
>>>
>>> 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}}
>>
>> There seems to be a superfluous space character before the colon, but I
>> don't think it matters much.
>>
>>>  #
>>>  ##
>>>  { '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;
>>>  out:
>>>      g_free(pdh_data);
>>>      g_free(cert_chain_data);
>>>
>>
>> Reviewed-by: Laszlo Ersek <address@hidden>
> 
> As mentioned in v1, I don't think a management application should need
> to run QEMU in order to figure this out.

Sorry, I didn't mean to ignore your feedback; I hadn't seen it.

Thanks
Laszlo