[PATCH 1/2] xen/*/nospec: Provide common versions of evaluate_nospec/block_speculation

[Andrew Cooper <andrew.cooper3@citrix.com>]

It is daft to require all architectures to provide empty implementations of
this functionality.

Provide evaluate_nospec() and block_speculation() unconditionally in
xen/nospec.h with architectures able to opt in by providing suitable arch
variants.

Rename x86's implementation to the arch_*() variants.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien@xen.org>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
CC: Bertrand Marquis <bertrand.marquis@arm.com>
CC: Michal Orzel <michal.orzel@amd.com>
CC: Oleksii Kurochko <oleksii.kurochko@gmail.com>
CC: Shawn Anastasio <sanastasio@raptorengineering.com>
---
 xen/arch/arm/include/asm/nospec.h   |  9 ---------
 xen/arch/ppc/include/asm/nospec.h   |  9 ---------
 xen/arch/riscv/include/asm/nospec.h |  9 ---------
 xen/arch/x86/include/asm/nospec.h   |  8 ++++----
 xen/include/xen/nospec.h            | 23 +++++++++++++++++++++++
 5 files changed, 27 insertions(+), 31 deletions(-)

diff --git a/xen/arch/arm/include/asm/nospec.h b/xen/arch/arm/include/asm/nospec.h
index efac51fc03be..05df096faab0 100644
--- a/xen/arch/arm/include/asm/nospec.h
+++ b/xen/arch/arm/include/asm/nospec.h
@@ -12,15 +12,6 @@
 # error "unknown ARM variant"
 #endif
 
-static inline bool evaluate_nospec(bool condition)
-{
-    return condition;
-}
-
-static inline void block_speculation(void)
-{
-}
-
 #endif /* _ASM_ARM_NOSPEC_H */
 
 /*
diff --git a/xen/arch/ppc/include/asm/nospec.h b/xen/arch/ppc/include/asm/nospec.h
index b97322e48d32..9b57a7e4b24d 100644
--- a/xen/arch/ppc/include/asm/nospec.h
+++ b/xen/arch/ppc/include/asm/nospec.h
@@ -3,13 +3,4 @@
 #ifndef __ASM_PPC_NOSPEC_H__
 #define __ASM_PPC_NOSPEC_H__
 
-static inline bool evaluate_nospec(bool condition)
-{
-    return condition;
-}
-
-static inline void block_speculation(void)
-{
-}
-
 #endif /* __ASM_PPC_NOSPEC_H__ */
diff --git a/xen/arch/riscv/include/asm/nospec.h b/xen/arch/riscv/include/asm/nospec.h
index e30f0a781b68..b227fc61ed8b 100644
--- a/xen/arch/riscv/include/asm/nospec.h
+++ b/xen/arch/riscv/include/asm/nospec.h
@@ -4,15 +4,6 @@
 #ifndef _ASM_RISCV_NOSPEC_H
 #define _ASM_RISCV_NOSPEC_H
 
-static inline bool evaluate_nospec(bool condition)
-{
-    return condition;
-}
-
-static inline void block_speculation(void)
-{
-}
-
 #endif /* _ASM_RISCV_NOSPEC_H */
 
 /*
diff --git a/xen/arch/x86/include/asm/nospec.h b/xen/arch/x86/include/asm/nospec.h
index 07606834c4c9..defc97707f03 100644
--- a/xen/arch/x86/include/asm/nospec.h
+++ b/xen/arch/x86/include/asm/nospec.h
@@ -23,20 +23,20 @@ static always_inline bool barrier_nospec_false(void)
     return false;
 }
 
-/* Allow to protect evaluation of conditionals with respect to speculation */
-static always_inline bool evaluate_nospec(bool condition)
+static always_inline bool arch_evaluate_nospec(bool condition)
 {
     if ( condition )
         return barrier_nospec_true();
     else
         return barrier_nospec_false();
 }
+#define arch_evaluate_nospec arch_evaluate_nospec
 
-/* Allow to block speculative execution in generic code */
-static always_inline void block_speculation(void)
+static always_inline void arch_block_speculation(void)
 {
     barrier_nospec_true();
 }
+#define arch_block_speculation arch_block_speculation
 
 /**
  * array_index_mask_nospec() - generate a mask that is ~0UL when the
diff --git a/xen/include/xen/nospec.h b/xen/include/xen/nospec.h
index 4c250ebbd663..a4155af08770 100644
--- a/xen/include/xen/nospec.h
+++ b/xen/include/xen/nospec.h
@@ -9,6 +9,29 @@
 
 #include <asm/nospec.h>
 
+/*
+ * Protect a conditional branch from bad speculation.  Architectures *must*
+ * provide arch_evaluate_nospec() for this to be effective.
+ */
+static always_inline bool evaluate_nospec(bool cond)
+{
+#ifndef arch_evaluate_nospec
+#define arch_evaluate_nospec(cond) cond
+#endif
+    return arch_evaluate_nospec(cond);
+}
+
+/*
+ * Halt speculation unconditonally.  Architectures *must* provide
+ * arch_block_speculation() for this to be effective.
+ */
+static always_inline void block_speculation(void)
+{
+#ifdef arch_block_speculation
+    arch_block_speculation();
+#endif
+}
+
 /**
  * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
  * @index: array element index
-- 
2.30.2