[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH] sev: allow capabilities to check for SEV-ES support

From: Tyler Fanelli
Subject: Re: [PATCH] sev: allow capabilities to check for SEV-ES support
Date: Tue, 16 Nov 2021 10:29:35 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0

On 11/16/21 4:17 AM, Daniel P. Berrangé wrote:
On Mon, Nov 15, 2021 at 02:38:04PM -0500, Tyler Fanelli wrote:
Probe for SEV-ES and SEV-SNP capabilities to distinguish between Rome,
Naples, and Milan processors. Use the CPUID function to probe if a
processor is capable of running SEV-ES or SEV-SNP, rather than if it
actually is running SEV-ES or SEV-SNP.

Signed-off-by: Tyler Fanelli <tfanelli@redhat.com>
  qapi/misc-target.json | 11 +++++++++--
  target/i386/sev.c     |  6 ++++--
  2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/qapi/misc-target.json b/qapi/misc-target.json
index 5aa2b95b7d..c3e9bce12b 100644
--- a/qapi/misc-target.json
+++ b/qapi/misc-target.json
@@ -182,13 +182,19 @@
  # @reduced-phys-bits: Number of physical Address bit reduction when SEV is
  #                     enabled
+# @es: SEV-ES capability of the machine.
+# @snp: SEV-SNP capability of the machine.
  # Since: 2.12
  { 'struct': 'SevCapability',
    'data': { 'pdh': 'str',
              'cert-chain': 'str',
              'cbitpos': 'int',
-            'reduced-phys-bits': 'int'},
+            'reduced-phys-bits': 'int',
+            'es': 'bool',
+            'snp': 'bool'},
    'if': 'TARGET_I386' }
@@ -205,7 +211,8 @@
  # -> { "execute": "query-sev-capabilities" }
  # <- { "return": { "pdh": "8CCDD8DDD", "cert-chain": "888CCCDDDEE",
-#                  "cbitpos": 47, "reduced-phys-bits": 5}}
+#                  "cbitpos": 47, "reduced-phys-bits": 5
+#                  "es": false, "snp": false}}
We've previously had patches posted to support SNP in QEMU


and this included an update to query-sev for reporting info
about the VM instance.

Your patch is updating query-sev-capabilities, which is a
counterpart for detecting host capabilities separate from
a guest instance.

Yes, that's because with this patch, I'm more interested in determining which AMD processor is running on a host, and less if ES or SNP is actually running on a guest instance or not.

None the less I wonder if the same design questions from
query-sev apply. ie do we need to have the ability to
report any SNP specific information fields, if so we need
to use a discriminated union of structs, not just bool

More generally I'm some what wary of adding this to
query-sev-capabilities at all, unless it is part of the
main SEV-SNP series.

Also what's the intended usage for the mgmt app from just
having these boolean fields ? Are they other more explicit
feature flags we should be reporting, instead of what are
essentially SEV generation codenames.

If by "mgmt app" you're referring to sevctl, in order to determine which certificate chain to use (Naples vs Rome vs Milan ARK/ASK) we must query which processor we are running on. Although sevctl has a feature which can do this already, we cannot guarantee that sevctl is running on the same host that a VM is running on, so we must query this capability from QEMU. My logic was determining the processor would have been the following:

!es && !snp --> Naples

es && !snp --> Rome

es && snp --> Milan



Tyler Fanelli (tfanelli)

reply via email to

[Prev in Thread] Current Thread [Next in Thread]