[PATCH 1/2] x86: Make hvm_enabled a constant unless both PV and HVM are both compiled

[Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>]

PV-shim already has hvm_enabled optimised to false, but there's no
reason HVM-only builds can't benefit from the same optimisation as long
as we add a boot-time panic in case HVM support is missed. Many branches
go away, some in the potentially hot switch_cr3_cr4.

HVM-only:
  add/remove: 0/1 grow/shrink: 1/9 up/down: 1/-162 (-161)
  Function                                     old     new   delta
  arch_do_physinfo                              79      80      +1
  hvm_enabled                                    1       -      -1
  symbols_offsets                            30732   30728      -4
  symbols_names                             108029  108022      -7
  symbols_sorted_offsets                     60656   60648      -8
  flush_area_local                             571     562      -9
  switch_cr3_cr4                               311     300     -11
  init_xen_cap_info                             62      43     -19
  arch_sanitise_domain_config                  885     863     -22
  init_guest_cpu_policies                     1270    1247     -23
  hvm_domain_initialise                       1127    1069     -58
  Total: Before=3797004, After=3796843, chg -0.00%

With hvm_enabled const-ified, it's fine to take hvm_flush_guest_tlbs()
outside the CONFIG_HVM ifdef and remove the stub. They compile to the
same code after DCE.

Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
---
 xen/arch/x86/hvm/hvm.c             |  9 +++++++++
 xen/arch/x86/include/asm/hvm/hvm.h | 30 +++++++++++++++---------------
 2 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 4d37a93c57..da56944e74 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -72,7 +72,9 @@
 
 #include <compat/hvm/hvm_op.h>
 
+#ifdef CONFIG_PV
 bool __read_mostly hvm_enabled;
+#endif /* CONFIG_PV */
 
 #ifdef DBG_LEVEL_0
 unsigned int opt_hvm_debug_level __read_mostly;
@@ -173,9 +175,16 @@ static int __init cf_check hvm_enable(void)
         svm_fill_funcs();
 
     if ( fns == NULL )
+    {
+        if ( !IS_ENABLED(CONFIG_PV) )
+            panic("HVM support not detected and PV compiled-out\n");
+
         return 0;
+    }
 
+#ifdef CONFIG_PV
     hvm_enabled = 1;
+#endif /* CONFIG_PV */
 
     printk("HVM: %s enabled\n", fns->name);
     if ( !hap_supported(&hvm_funcs) )
diff --git a/xen/arch/x86/include/asm/hvm/hvm.h 
b/xen/arch/x86/include/asm/hvm/hvm.h
index 7d9774df59..dc609bf4cb 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -261,7 +261,11 @@ struct hvm_function_table {
 };
 
 extern struct hvm_function_table hvm_funcs;
+#if defined(CONFIG_PV) && defined(CONFIG_HVM)
 extern bool hvm_enabled;
+#else
+#define hvm_enabled IS_ENABLED(CONFIG_HVM)
+#endif
 extern int8_t hvm_port80_allowed;
 
 extern const struct hvm_function_table *start_svm(void);
@@ -399,6 +403,17 @@ static inline bool using_svm(void)
 #define hvm_is_in_uc_mode(d) \
     (using_vmx() && (d)->arch.hvm.vmx.in_uc_mode)
 
+/*
+ * Called to ensure than all guest-specific mappings in a tagged TLB are
+ * flushed; does *not* flush Xen's TLB entries, and on processors without a
+ * tagged TLB it will be a noop.
+ */
+static inline void hvm_flush_guest_tlbs(void)
+{
+    if ( hvm_enabled )
+        hvm_asid_flush_core();
+}
+
 #ifdef CONFIG_HVM
 
 #define hvm_get_guest_tsc(v) hvm_get_guest_tsc_fixed(v, 0)
@@ -498,17 +513,6 @@ static inline void hvm_set_tsc_offset(struct vcpu *v, 
uint64_t offset)
     alternative_vcall(hvm_funcs.set_tsc_offset, v, offset);
 }
 
-/*
- * Called to ensure than all guest-specific mappings in a tagged TLB are 
- * flushed; does *not* flush Xen's TLB entries, and on processors without a 
- * tagged TLB it will be a noop.
- */
-static inline void hvm_flush_guest_tlbs(void)
-{
-    if ( hvm_enabled )
-        hvm_asid_flush_core();
-}
-
 static inline unsigned int
 hvm_get_cpl(struct vcpu *v)
 {
@@ -854,8 +858,6 @@ static inline void hvm_sync_pir_to_irr(struct vcpu *v)
 
 #else  /* CONFIG_HVM */
 
-#define hvm_enabled false
-
 /*
  * List of inline functions above, of which only declarations are
  * needed because DCE will kick in.
@@ -902,8 +904,6 @@ static inline int hvm_cpu_up(void)
 
 static inline void hvm_cpu_down(void) {}
 
-static inline void hvm_flush_guest_tlbs(void) {}
-
 static inline void hvm_invlpg(const struct vcpu *v, unsigned long linear)
 {
     ASSERT_UNREACHABLE();
-- 
2.43.0