[Xen-devel] [PATCH 1/3] x86/alternatives: fully leverage automatic NOP filling

["Jan Beulich" <JBeulich@xxxxxxxx>]

As of commit 4008c71d7a ("x86/alt: Support for automatic padding
calculations") there's no point having explict ASM_NOPn instances in
alternatives anymore - drop them. As a result also drop the asm/nops.h
inclusion from alternative.h, adding explicit inclusions in the two
remaining C files needing them.

While touching it also move the CR4_PV32_RESTORE definition out of the
SMAP-specific conditional into a more general one.

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

--- a/xen/arch/x86/alternative.c
+++ b/xen/arch/x86/alternative.c
@@ -24,6 +24,7 @@
 #include <asm/system.h>
 #include <asm/traps.h>
 #include <asm/nmi.h>
+#include <asm/nops.h>
 #include <xen/livepatch.h>
 
 #define MAX_PATCH_LEN (255-1)
--- a/xen/arch/x86/flushtlb.c
+++ b/xen/arch/x86/flushtlb.c
@@ -10,6 +10,7 @@
 #include <xen/sched.h>
 #include <xen/softirq.h>
 #include <asm/flushtlb.h>
+#include <asm/nops.h>
 #include <asm/page.h>
 
 /* Debug builds: Wrap frequently to stress-test the wrap logic. */
@@ -143,7 +144,7 @@ unsigned int flush_area_local(const void
              c->x86_clflush_size && c->x86_cache_size && sz &&
              ((sz >> 10) < c->x86_cache_size) )
         {
-            alternative(ASM_NOP3, "sfence", X86_FEATURE_CLFLUSHOPT);
+            alternative("", "sfence", X86_FEATURE_CLFLUSHOPT);
             for ( i = 0; i < sz; i += c->x86_clflush_size )
                 alternative_input(".byte " __stringify(NOP_DS_PREFIX) ";"
                                   " clflush %0",
--- a/xen/include/asm-x86/alternative.h
+++ b/xen/include/asm-x86/alternative.h
@@ -2,7 +2,6 @@
 #define __X86_ALTERNATIVE_H__
 
 #include <asm/alternative-asm.h>
-#include <asm/nops.h>
 
 #ifndef __ASSEMBLY__
 #include <xen/stringify.h>
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -195,30 +195,19 @@ void ret_from_intr(void);
 #define __ASM_STAC      .byte 0x0f,0x01,0xcb
 
 #ifdef __ASSEMBLY__
-#define ASM_STAC                                        \
-    ALTERNATIVE __stringify(ASM_NOP3),                  \
-        __stringify(__ASM_STAC), X86_FEATURE_XEN_SMAP
-
-#define ASM_CLAC                                        \
-    ALTERNATIVE __stringify(ASM_NOP3),                  \
-        __stringify(__ASM_CLAC), X86_FEATURE_XEN_SMAP
-
-#define CR4_PV32_RESTORE                                \
-    ALTERNATIVE_2 __stringify(ASM_NOP5),                \
-        "call cr4_pv32_restore", X86_FEATURE_XEN_SMEP,  \
-        "call cr4_pv32_restore", X86_FEATURE_XEN_SMAP
-
+#define ASM_STAC ALTERNATIVE "", __stringify(__ASM_STAC), X86_FEATURE_XEN_SMAP
+#define ASM_CLAC ALTERNATIVE "", __stringify(__ASM_CLAC), X86_FEATURE_XEN_SMAP
 #else
 static always_inline void clac(void)
 {
     /* Note: a barrier is implicit in alternative() */
-    alternative(ASM_NOP3, __stringify(__ASM_CLAC), X86_FEATURE_XEN_SMAP);
+    alternative("", __stringify(__ASM_CLAC), X86_FEATURE_XEN_SMAP);
 }
 
 static always_inline void stac(void)
 {
     /* Note: a barrier is implicit in alternative() */
-    alternative(ASM_NOP3, __stringify(__ASM_STAC), X86_FEATURE_XEN_SMAP);
+    alternative("", __stringify(__ASM_STAC), X86_FEATURE_XEN_SMAP);
 }
 #endif
 
@@ -327,6 +316,11 @@ static always_inline void stac(void)
         subq  $-(UREGS_error_code-UREGS_r15+\adj), %rsp
 .endm
 
+#define CR4_PV32_RESTORE                               \
+    ALTERNATIVE_2 "",                                  \
+        "call cr4_pv32_restore", X86_FEATURE_XEN_SMEP, \
+        "call cr4_pv32_restore", X86_FEATURE_XEN_SMAP
+
 #endif
 
 #ifdef CONFIG_PERF_COUNTERS
--- a/xen/include/asm-x86/spec_ctrl.h
+++ b/xen/include/asm-x86/spec_ctrl.h
@@ -50,7 +50,7 @@ static always_inline void spec_ctrl_ente
     barrier();
     info->use_shadow_spec_ctrl = true;
     barrier();
-    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_XEN_IBRS_SET)
+    asm volatile ( ALTERNATIVE("", "wrmsr", X86_FEATURE_XEN_IBRS_SET)
                    :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
 }
 
@@ -65,7 +65,7 @@ static always_inline void spec_ctrl_exit
      */
     info->use_shadow_spec_ctrl = false;
     barrier();
-    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_XEN_IBRS_SET)
+    asm volatile ( ALTERNATIVE("", "wrmsr", X86_FEATURE_XEN_IBRS_SET)
                    :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
 }
 



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