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

[Singh, Brijesh]

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 <pbonz...@redhat.com>
Cc: Markus Armbruster <arm...@redhat.com>
Cc: Eric Blake <ebl...@redhat.com>
Cc: Daniel P. Berrangé <berra...@redhat.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Cc: Erik Skultety <eskul...@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.si...@amd.com>
---
 qapi/target.json  | 6 ++++--
 target/i386/sev.c | 6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/qapi/target.json b/qapi/target.json
index 1d4d54b600..b45121d30b 100644
--- a/qapi/target.json
+++ b/qapi/target.json
@@ -183,7 +183,8 @@
   '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 +201,8 @@
 #
 # -> { "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..bb0cd79acd 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 +516,8 @@ sev_get_capabilities(void)
      */
     cap->reduced_phys_bits = 1;
 
+    /* the maximum number of SEV guests that can run simultaneously */
+    cap->sev_max_guests = ecx - edx + 1;
 out:
     g_free(pdh_data);
     g_free(cert_chain_data);
-- 
2.17.1