qemu: report max number of SEV guests

Different CPU generations have different limits on the number
of SEV/SEV-ES guests that can be run. Since both limits come
from the same overall set, there is typically also BIOS config
to set the tradeoff betweeen SEV and SEV-ES guest limits.

This is important information to expose for a mgmt application
scheduling guests to hosts.

Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/qemu/qemu_capabilities.c

@@ -1897,6 +1897,8 @@ virQEMUCapsSEVInfoCopy(virSEVCapability **dst,
 
     tmp->cbitpos = src->cbitpos;
     tmp->reduced_phys_bits = src->reduced_phys_bits;
+    tmp->max_guests = src->max_guests;
+    tmp->max_es_guests = src->max_es_guests;
 
     *dst = g_steal_pointer(&tmp);
     return 0;
@@ -3286,6 +3288,31 @@ virQEMUCapsProbeQMPGICCapabilities(virQEMUCaps *qemuCaps,
 }
 
 
+static void
+virQEMUCapsGetSEVMaxGuests(virSEVCapability *caps)
+{
+    /*
+     * From Secure Encrypted Virtualization API v0.24, section 6.19.1
+     *
+     * If the guest is SEV-ES enabled, then the ASID must be at least
+     * 1h and at most (MIN_SEV_ASID-1). If the guest is not SEV-ES
+     * enabled, then the ASID must be at least MIN_SEV_ASID and at
+     * most the maximum SEV ASID available. The MIN_SEV_ASID value
+     * is discovered by CPUID Fn8000_001F[EDX]. The maximum SEV ASID
+     * available is discovered by CPUID Fn8000_001F[ECX].
+     */
+    uint32_t min_asid, max_asid;
+    virHostCPUX86GetCPUID(0x8000001F, 0, NULL, NULL,
+                          &max_asid, &min_asid);
+
+    if (max_asid != 0 && min_asid != 0) {
+        caps->max_guests = max_asid - min_asid + 1;
+        caps->max_es_guests = min_asid - 1;
+    } else {
+        caps->max_guests = caps->max_es_guests = 0;
+    }
+}
+
 static int
 virQEMUCapsProbeQMPSEVCapabilities(virQEMUCaps *qemuCaps,
                                    qemuMonitor *mon)
@@ -3305,6 +3332,8 @@ virQEMUCapsProbeQMPSEVCapabilities(virQEMUCaps *qemuCaps,
         return 0;
     }
 
+    virQEMUCapsGetSEVMaxGuests(caps);
+
     virSEVCapabilitiesFree(qemuCaps->sevCapabilities);
     qemuCaps->sevCapabilities = caps;
     return 0;
@@ -4084,6 +4113,14 @@ virQEMUCapsParseSEVInfo(virQEMUCaps *qemuCaps, xmlXPathContextPtr ctxt)
         return -1;
     }
 
+
+    /* We probe this every time because the values
+     * can change on every reboot via firmware
+     * config tunables. It is cheap to query so
+     * lack of caching is a non-issue
+     */
+    virQEMUCapsGetSEVMaxGuests(sev);
+
     qemuCaps->sevCapabilities = g_steal_pointer(&sev);
     return 0;
 }
@@ -6344,6 +6381,8 @@ virQEMUCapsFillDomainFeatureSEVCaps(virQEMUCaps *qemuCaps,
     domCaps->sev->cert_chain = g_strdup(cap->cert_chain);
     domCaps->sev->cbitpos = cap->cbitpos;
     domCaps->sev->reduced_phys_bits = cap->reduced_phys_bits;
+    domCaps->sev->max_guests = cap->max_guests;
+    domCaps->sev->max_es_guests = cap->max_es_guests;
 }
 
 

src/qemu/qemu_driver.c

@@ -19917,6 +19917,16 @@ qemuGetSEVInfoToParams(virQEMUCaps *qemuCaps,
                     sev->reduced_phys_bits) < 0)
         goto cleanup;
 
+    if (virTypedParamsAddUInt(&sevParams, &n, &maxpar,
+                    VIR_NODE_SEV_MAX_GUESTS,
+                    sev->max_guests) < 0)
+        goto cleanup;
+
+    if (virTypedParamsAddUInt(&sevParams, &n, &maxpar,
+                    VIR_NODE_SEV_MAX_ES_GUESTS,
+                    sev->max_es_guests) < 0)
+        goto cleanup;
+
     *params = g_steal_pointer(&sevParams);
     *nparams = n;
     return 0;

tests/domaincapsdata/qemu_2.12.0-q35.x86_64.xml

@@ -205,8 +205,8 @@
     <sev supported='yes'>
       <cbitpos>47</cbitpos>
       <reducedPhysBits>1</reducedPhysBits>
-      <maxGuests>0</maxGuests>
+      <maxGuests>59</maxGuests>
-      <maxESGuests>0</maxESGuests>
+      <maxESGuests>450</maxESGuests>
     </sev>
   </features>
 </domainCapabilities>

tests/domaincapsdata/qemu_2.12.0-tcg.x86_64.xml

@@ -215,8 +215,8 @@
     <sev supported='yes'>
       <cbitpos>47</cbitpos>
       <reducedPhysBits>1</reducedPhysBits>
-      <maxGuests>0</maxGuests>
+      <maxGuests>59</maxGuests>
-      <maxESGuests>0</maxESGuests>
+      <maxESGuests>450</maxESGuests>
     </sev>
   </features>
 </domainCapabilities>

tests/domaincapsdata/qemu_2.12.0.x86_64.xml

@@ -205,8 +205,8 @@
     <sev supported='yes'>
       <cbitpos>47</cbitpos>
       <reducedPhysBits>1</reducedPhysBits>
-      <maxGuests>0</maxGuests>
+      <maxGuests>59</maxGuests>
-      <maxESGuests>0</maxESGuests>
+      <maxESGuests>450</maxESGuests>
     </sev>
   </features>
 </domainCapabilities>

tests/domaincapsdata/qemu_6.0.0-q35.x86_64.xml

@@ -227,8 +227,8 @@
     <sev supported='yes'>
       <cbitpos>47</cbitpos>
       <reducedPhysBits>1</reducedPhysBits>
-      <maxGuests>0</maxGuests>
+      <maxGuests>59</maxGuests>
-      <maxESGuests>0</maxESGuests>
+      <maxESGuests>450</maxESGuests>
     </sev>
   </features>
 </domainCapabilities>

tests/domaincapsdata/qemu_6.0.0-tcg.x86_64.xml

@@ -233,8 +233,8 @@
     <sev supported='yes'>
       <cbitpos>47</cbitpos>
       <reducedPhysBits>1</reducedPhysBits>
-      <maxGuests>0</maxGuests>
+      <maxGuests>59</maxGuests>
-      <maxESGuests>0</maxESGuests>
+      <maxESGuests>450</maxESGuests>
     </sev>
   </features>
 </domainCapabilities>

tests/domaincapsdata/qemu_6.0.0.x86_64.xml

@@ -227,8 +227,8 @@
     <sev supported='yes'>
       <cbitpos>47</cbitpos>
       <reducedPhysBits>1</reducedPhysBits>
-      <maxGuests>0</maxGuests>
+      <maxGuests>59</maxGuests>
-      <maxESGuests>0</maxESGuests>
+      <maxESGuests>450</maxESGuests>
     </sev>
   </features>
 </domainCapabilities>

tests/testutilsqemu.c

@@ -143,6 +143,29 @@ virCapabilitiesHostNUMANewHost(void)
     return virTestCapsBuildNUMATopology(3);
 }
 
+void
+virHostCPUX86GetCPUID(uint32_t leaf,
+                      uint32_t extended,
+                      uint32_t *eax,
+                      uint32_t *ebx,
+                      uint32_t *ecx,
+                      uint32_t *edx)
+{
+    if (eax)
+        *eax = 0;
+    if (ebx)
+        *ebx = 0;
+    if (ecx)
+        *ecx = 0;
+    if (edx)
+        *edx = 0;
+    if (leaf == 0x8000001F && extended == 0) {
+        if (ecx)
+            *ecx = 509;
+        if (edx)
+            *edx = 451;
+    }
+}
 
 static int
 testQemuAddGuest(virCaps *caps,