x86/cpuid: Split dom0 handling out of init_domain_cpuid_policy()

To implement dom0-cpuid= support, the special cases would need extending.
However there is already a problem with late hwdom where the special cases
override toolstack settings, which is unintended and poor behaviour.

Introduce a new init_dom0_cpuid_policy() for the purpose, moving the ITSC and
ARCH_CAPS logic.  The is_hardware_domain() can be dropped, and for now there
is no need to rerun recalculate_cpuid_policy(); this is a relatively expensive
operation, and will become more-so over time.

Rearrange the logic in create_dom0() to make room for a call to
init_dom0_cpuid_policy().  The AMX plans for having variable sized XSAVE
states require that modifications to the policy happen before vCPUs are
created.

Additionally, factor out domid into a variable so we can be slightly more
correct in the case of a failure, and also print the error from
domain_create().  This will at least help distinguish -EINVAL from -ENOMEM.

No practical change in behaviour.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit c17072fc16)

xen/arch/x86/cpuid.c

@@ -744,22 +744,28 @@ int init_domain_cpuid_policy(struct domain *d)
     if ( !p )
         return -ENOMEM;
 
-    if ( d->disable_migrate )
-        p->extd.itsc = cpu_has_itsc;
+    d->arch.cpuid = p;
+
+    recalculate_cpuid_policy(d);
+
+    return 0;
+}
+
+void __init init_dom0_cpuid_policy(struct domain *d)
+{
+    struct cpuid_policy *p = d->arch.cpuid;
+
+    /* dom0 can't migrate.  Give it ITSC if available. */
+    if ( cpu_has_itsc )
+        p->extd.itsc = true;
 
     /*
      * Expose the "hardware speculation behaviour" bits of ARCH_CAPS to dom0,
      * so dom0 can turn off workarounds as appropriate.  Temporary, until the
      * domain policy logic gains a better understanding of MSRs.
      */
-    if ( is_hardware_domain(d) && cpu_has_arch_caps )
+    if ( cpu_has_arch_caps )
         p->feat.arch_caps = true;
-
-    d->arch.cpuid = p;
-
-    recalculate_cpuid_policy(d);
-
-    return 0;
 }
 
 void guest_cpuid(const struct vcpu *v, uint32_t leaf,

xen/arch/x86/setup.c

@@ -770,6 +770,7 @@ static struct domain *__init create_dom0(const module_t *image,
     };
     struct domain *d;
     char *cmdline;
+    domid_t domid;
 
     if ( opt_dom0_pvh )
     {
@@ -784,10 +785,16 @@ static struct domain *__init create_dom0(const module_t *image,
     if ( iommu_enabled )
         dom0_cfg.flags |= XEN_DOMCTL_CDF_iommu;
 
-    /* Create initial domain 0. */
-    d = domain_create(get_initial_domain_id(), &dom0_cfg, !pv_shim);
-    if ( IS_ERR(d) || (alloc_dom0_vcpu0(d) == NULL) )
-        panic("Error creating domain 0\n");
+    /* Create initial domain.  Not d0 for pvshim. */
+    domid = get_initial_domain_id();
+    d = domain_create(domid, &dom0_cfg, !pv_shim);
+    if ( IS_ERR(d) )
+        panic("Error creating d%u: %ld\n", domid, PTR_ERR(d));
+
+    init_dom0_cpuid_policy(d);
+
+    if ( alloc_dom0_vcpu0(d) == NULL )
+        panic("Error creating d%uv0\n", domid);
 
     /* Grab the DOM0 command line. */
     cmdline = image->string ? __va(image->string) : NULL;

xen/include/asm-x86/cpuid.h

@@ -59,6 +59,9 @@ bool recheck_cpu_features(unsigned int cpu);
 /* Allocate and initialise a CPUID policy suitable for the domain. */
 int init_domain_cpuid_policy(struct domain *d);
 
+/* Apply dom0-specific tweaks to the CPUID policy. */
+void init_dom0_cpuid_policy(struct domain *d);
+
 /* Clamp the CPUID policy to reality. */
 void recalculate_cpuid_policy(struct domain *d);