[PATCH] domain: adjust soft-reset arch dependency

[Jan Beulich <jbeulich@xxxxxxxx>]

Arm's arch_domain_soft_reset() returning -ENOSYS is quite unhelpful: This
way a domain will be crashed if a tool stack mistakenly invokes
XEN_DOMCTL_soft_reset on it. Instead the tool stack should be told of its
mistake.

Introduce HAS_SOFT_RESET, implied only by x86. "imply" rather than
"select" such that HAS_SOFT_RESET can later gain a dependency on
MGMT_HYPERCALLS. That way HAS_SOFT_RESET will go off when
MGMT_HYPERCALLS is off.

Check the new setting early in domctl handling, and compile out the thus
dead (when HAS_SOFT_RESET=n) domain_soft_reset() as well as its dedicated
helpers.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -875,11 +875,6 @@ void arch_domain_unpause(struct domain *
 {
 }
 
-int arch_domain_soft_reset(struct domain *d)
-{
-    return -ENOSYS;
-}
-
 void arch_domain_creation_finished(struct domain *d)
 {
     p2m_domain_creation_finished(d);
--- a/xen/arch/ppc/stubs.c
+++ b/xen/arch/ppc/stubs.c
@@ -214,11 +214,6 @@ void arch_domain_unpause(struct domain *
     BUG_ON("unimplemented");
 }
 
-int arch_domain_soft_reset(struct domain *d)
-{
-    BUG_ON("unimplemented");
-}
-
 void arch_domain_creation_finished(struct domain *d)
 {
     BUG_ON("unimplemented");
--- a/xen/arch/riscv/stubs.c
+++ b/xen/arch/riscv/stubs.c
@@ -188,11 +188,6 @@ void arch_domain_unpause(struct domain *
     BUG_ON("unimplemented");
 }
 
-int arch_domain_soft_reset(struct domain *d)
-{
-    BUG_ON("unimplemented");
-}
-
 void arch_domain_creation_finished(struct domain *d)
 {
     BUG_ON("unimplemented");
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -29,6 +29,7 @@ config X86
        select HAS_PCI_MSI
        select HAS_PIRQ
        select HAS_SCHED_GRANULARITY
+       imply HAS_SOFT_RESET
        select HAS_UBSAN
        select HAS_VMAP
        select HAS_VPCI if HVM
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1030,6 +1030,7 @@ void arch_domain_unpause(struct domain *
         viridian_time_domain_thaw(d);
 }
 
+#ifdef CONFIG_HAS_SOFT_RESET
 int arch_domain_soft_reset(struct domain *d)
 {
     struct page_info *page = virt_to_page(d->shared_info), *new_page;
@@ -1131,6 +1132,7 @@ int arch_domain_soft_reset(struct domain
 
     return ret;
 }
+#endif /* CONFIG_HAS_SOFT_RESET */
 
 void arch_domain_creation_finished(struct domain *d)
 {
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -155,6 +155,9 @@ config HAS_PMAP
 config HAS_SCHED_GRANULARITY
        bool
 
+config HAS_SOFT_RESET
+       bool
+
 config HAS_STACK_PROTECTOR
        bool
 
--- a/xen/common/argo.c
+++ b/xen/common/argo.c
@@ -2351,6 +2351,7 @@ argo_destroy(struct domain *d)
     write_unlock(&L1_global_argo_rwlock);
 }
 
+#ifdef CONFIG_HAS_SOFT_RESET
 void
 argo_soft_reset(struct domain *d)
 {
@@ -2374,3 +2375,4 @@ argo_soft_reset(struct domain *d)
 
     write_unlock(&L1_global_argo_rwlock);
 }
+#endif /* CONFIG_HAS_SOFT_RESET */
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1687,6 +1687,7 @@ void domain_unpause_except_self(struct d
         domain_unpause(d);
 }
 
+#ifdef CONFIG_HAS_SOFT_RESET
 int domain_soft_reset(struct domain *d, bool resuming)
 {
     struct vcpu *v;
@@ -1724,6 +1725,7 @@ int domain_soft_reset(struct domain *d,
 
     return rc;
 }
+#endif /* CONFIG_HAS_SOFT_RESET */
 
 int vcpu_reset(struct vcpu *v)
 {
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -466,6 +466,12 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
 
     case XEN_DOMCTL_soft_reset:
     case XEN_DOMCTL_soft_reset_cont:
+        if ( !IS_ENABLED(CONFIG_HAS_SOFT_RESET) )
+        {
+            ret = -EOPNOTSUPP;
+            break;
+        }
+
         if ( d == current->domain ) /* no domain_pause() */
         {
             ret = -EINVAL;
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -3962,6 +3962,7 @@ int gnttab_release_mappings(struct domai
     return 0;
 }
 
+#ifdef CONFIG_HAS_SOFT_RESET
 void grant_table_warn_active_grants(struct domain *d)
 {
     struct grant_table *gt = d->grant_table;
@@ -4006,6 +4007,7 @@ void grant_table_warn_active_grants(stru
 
 #undef WARN_GRANT_MAX
 }
+#endif /* CONFIG_HAS_SOFT_RESET */
 
 void
 grant_table_destroy(