# Commit af949407eaba7af71067f23d5866cd0bf1f1144d
# Date 2018-05-16 12:19:10 +0100
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
x86/spec_ctrl: Fold the XEN_IBRS_{SET,CLEAR} ALTERNATIVES together

Currently, the SPEC_CTRL_{ENTRY,EXIT}_* macros encode Xen's choice of
MSR_SPEC_CTRL as an immediate constant, and chooses between IBRS or not by
doubling up the entire alternative block.

There is now a variable holding Xen's choice of value, so use that and
simplify the alternatives.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -357,13 +357,9 @@ void __cpuinit identify_cpu(struct cpuin
 		if (test_bit(X86_FEATURE_IND_THUNK_JMP,
 			     boot_cpu_data.x86_capability))
 			__set_bit(X86_FEATURE_IND_THUNK_JMP, c->x86_capability);
-		if (test_bit(X86_FEATURE_XEN_IBRS_SET,
+		if (test_bit(X86_FEATURE_SC_MSR,
 		             boot_cpu_data.x86_capability))
-			__set_bit(X86_FEATURE_XEN_IBRS_SET, c->x86_capability);
-		if (test_bit(X86_FEATURE_XEN_IBRS_CLEAR,
-		             boot_cpu_data.x86_capability))
-			__set_bit(X86_FEATURE_XEN_IBRS_CLEAR,
-			          c->x86_capability);
+			__set_bit(X86_FEATURE_SC_MSR, c->x86_capability);
 		if (test_bit(X86_FEATURE_RSB_NATIVE,
 		             boot_cpu_data.x86_capability))
 			__set_bit(X86_FEATURE_RSB_NATIVE, c->x86_capability);
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -114,8 +114,9 @@ static void __init print_details(enum in
            thunk == THUNK_RETPOLINE ? "RETPOLINE" :
            thunk == THUNK_LFENCE    ? "LFENCE" :
            thunk == THUNK_JMP       ? "JMP" : "?",
-           boot_cpu_has(X86_FEATURE_XEN_IBRS_SET)    ? " IBRS+" :
-           boot_cpu_has(X86_FEATURE_XEN_IBRS_CLEAR)  ? " IBRS-"      : "",
+           boot_cpu_has(X86_FEATURE_SC_MSR) ?
+           default_xen_spec_ctrl & SPEC_CTRL_IBRS    ? " IBRS+" :
+                                                       " IBRS-"      : "",
            opt_ibpb                                  ? " IBPB"       : "",
            boot_cpu_has(X86_FEATURE_RSB_NATIVE)      ? " RSB_NATIVE" : "",
            boot_cpu_has(X86_FEATURE_RSB_VMEXIT)      ? " RSB_VMEXIT" : "");
@@ -271,13 +272,10 @@ void __init init_speculation_mitigations
          * need the IBRS entry/exit logic to virtualise IBRS support for
          * guests.
          */
+        __set_bit(X86_FEATURE_SC_MSR, boot_cpu_data.x86_capability);
+
         if ( ibrs )
-        {
             default_xen_spec_ctrl |= SPEC_CTRL_IBRS;
-            __set_bit(X86_FEATURE_XEN_IBRS_SET, boot_cpu_data.x86_capability);
-        }
-        else
-            __set_bit(X86_FEATURE_XEN_IBRS_CLEAR, boot_cpu_data.x86_capability);
 
         default_spec_ctrl_flags |= SCF_ist_wrmsr;
     }
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -67,8 +67,7 @@
 #define X86_FEATURE_IND_THUNK_LFENCE (3*32+ 1) /* Use IND_THUNK_LFENCE */
 #define X86_FEATURE_IND_THUNK_JMP   (3*32+ 2) /* Use IND_THUNK_JMP */
 #define X86_FEATURE_XEN_IBPB        (3*32+ 3) /* IBRSB || IBPB */
-#define X86_FEATURE_XEN_IBRS_SET    (3*32+ 4) /* IBRSB && IRBS set in Xen */
-#define X86_FEATURE_XEN_IBRS_CLEAR  (3*32+ 5) /* IBRSB && IBRS clear in Xen */
+#define X86_FEATURE_SC_MSR          (3*32+ 4) /* MSR_SPEC_CTRL used by Xen */
 #define X86_FEATURE_MFENCE_RDTSC (3*32+ 7) /* MFENCE synchronizes RDTSC */
 #define X86_FEATURE_CONSTANT_TSC (3*32+ 8) /* TSC ticks at a constant rate */
 #define X86_FEATURE_NONSTOP_TSC	(3*32+ 9) /* TSC does not stop in C states */
--- a/xen/include/asm-x86/nops.h
+++ b/xen/include/asm-x86/nops.h
@@ -61,11 +61,12 @@
 #define ASM_NOP7 _ASM_MK_NOP(K8_NOP7)
 #define ASM_NOP8 _ASM_MK_NOP(K8_NOP8)
 
-#define ASM_NOP22 ASM_NOP8; ASM_NOP8; ASM_NOP6
 #define ASM_NOP23 ASM_NOP8; ASM_NOP8; ASM_NOP7
 #define ASM_NOP24 ASM_NOP8; ASM_NOP8; ASM_NOP8
-#define ASM_NOP32 ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP8
-#define ASM_NOP36 ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP4
+#define ASM_NOP25 ASM_NOP8; ASM_NOP8; ASM_NOP7; ASM_NOP2
+#define ASM_NOP33 ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP7; ASM_NOP2
+#define ASM_NOP34 ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP2
+#define ASM_NOP39 ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP7
 #define ASM_NOP40 ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP8; ASM_NOP8
 
 #define ASM_NOP_MAX 8
--- a/xen/include/asm-x86/spec_ctrl.h
+++ b/xen/include/asm-x86/spec_ctrl.h
@@ -54,14 +54,16 @@ static always_inline void spec_ctrl_ente
     barrier();
     info->spec_ctrl_flags |= SCF_use_shadow;
     barrier();
-    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_XEN_IBRS_SET)
-                   :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
+    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", %c3)
+                   :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0),
+                      "i" (X86_FEATURE_SC_MSR)
+                   : "memory" );
 }
 
 /* WARNING! `ret`, `call *`, `jmp *` not safe before this call. */
 static always_inline void spec_ctrl_exit_idle(struct cpu_info *info)
 {
-    uint32_t val = SPEC_CTRL_IBRS;
+    uint32_t val = info->xen_spec_ctrl;
 
     /*
      * Disable shadowing before updating the MSR.  There are no SMP issues
@@ -69,8 +71,10 @@ static always_inline void spec_ctrl_exit
      */
     info->spec_ctrl_flags &= ~SCF_use_shadow;
     barrier();
-    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_XEN_IBRS_SET)
-                   :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
+    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", %c3)
+                   :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0),
+                      "i" (X86_FEATURE_SC_MSR)
+                   : "memory" );
 }
 
 #endif /* !__X86_SPEC_CTRL_H__ */
--- a/xen/include/asm-x86/spec_ctrl_asm.h
+++ b/xen/include/asm-x86/spec_ctrl_asm.h
@@ -117,7 +117,7 @@
     mov %\tmp, %rsp                 /* Restore old %rsp */
 .endm
 
-.macro DO_SPEC_CTRL_ENTRY_FROM_VMEXIT ibrs_val:req
+.macro DO_SPEC_CTRL_ENTRY_FROM_VMEXIT
 /*
  * Requires %rbx=current, %rsp=regs/cpuinfo
  * Clobbers %rax, %rcx, %rdx
@@ -137,11 +137,11 @@
     andb $~SCF_use_shadow, CPUINFO_spec_ctrl_flags(%rsp)
 
     /* Load Xen's intended value. */
-    mov $\ibrs_val, %eax
+    movzbl CPUINFO_xen_spec_ctrl(%rsp), %eax
     wrmsr
 .endm
 
-.macro DO_SPEC_CTRL_ENTRY maybexen:req ibrs_val:req
+.macro DO_SPEC_CTRL_ENTRY maybexen:req
 /*
  * Requires %rsp=regs (also cpuinfo if !maybexen)
  * Requires %r14=stack_end (if maybexen)
@@ -166,12 +166,12 @@
         setnz %al
         not %eax
         and %al, STACK_CPUINFO_FIELD(spec_ctrl_flags)(%r14)
+        movzbl STACK_CPUINFO_FIELD(xen_spec_ctrl)(%r14), %eax
     .else
         andb $~SCF_use_shadow, CPUINFO_spec_ctrl_flags(%rsp)
+        movzbl CPUINFO_xen_spec_ctrl(%rsp), %eax
     .endif
 
-    /* Load Xen's intended value. */
-    mov $\ibrs_val, %eax
     wrmsr
 .endm
 
@@ -219,47 +219,32 @@
 #define SPEC_CTRL_ENTRY_FROM_VMEXIT                                     \
     ALTERNATIVE __stringify(ASM_NOP40),                                 \
         DO_OVERWRITE_RSB, X86_FEATURE_RSB_VMEXIT;                       \
-    ALTERNATIVE_2 __stringify(ASM_NOP33),                               \
-        __stringify(DO_SPEC_CTRL_ENTRY_FROM_VMEXIT                      \
-                    ibrs_val=SPEC_CTRL_IBRS),                           \
-        X86_FEATURE_XEN_IBRS_SET,                                       \
-        __stringify(DO_SPEC_CTRL_ENTRY_FROM_VMEXIT                      \
-                    ibrs_val=0),                                        \
-        X86_FEATURE_XEN_IBRS_CLEAR
+    ALTERNATIVE __stringify(ASM_NOP34),                                 \
+        DO_SPEC_CTRL_ENTRY_FROM_VMEXIT, X86_FEATURE_SC_MSR
 
 /* Use after an entry from PV context (syscall/sysenter/int80/int82/etc). */
 #define SPEC_CTRL_ENTRY_FROM_PV                                         \
     ALTERNATIVE __stringify(ASM_NOP40),                                 \
         DO_OVERWRITE_RSB, X86_FEATURE_RSB_NATIVE;                       \
-    ALTERNATIVE_2 __stringify(ASM_NOP22),                               \
-        __stringify(DO_SPEC_CTRL_ENTRY maybexen=0                       \
-                    ibrs_val=SPEC_CTRL_IBRS),                           \
-        X86_FEATURE_XEN_IBRS_SET,                                       \
-        __stringify(DO_SPEC_CTRL_ENTRY maybexen=0 ibrs_val=0),          \
-        X86_FEATURE_XEN_IBRS_CLEAR
+    ALTERNATIVE __stringify(ASM_NOP25),                                 \
+        __stringify(DO_SPEC_CTRL_ENTRY maybexen=0), X86_FEATURE_SC_MSR
 
 /* Use in interrupt/exception context.  May interrupt Xen or PV context. */
 #define SPEC_CTRL_ENTRY_FROM_INTR                                       \
     ALTERNATIVE __stringify(ASM_NOP40),                                 \
         DO_OVERWRITE_RSB, X86_FEATURE_RSB_NATIVE;                       \
-    ALTERNATIVE_2 __stringify(ASM_NOP36),                               \
-        __stringify(DO_SPEC_CTRL_ENTRY maybexen=1                       \
-                    ibrs_val=SPEC_CTRL_IBRS),                           \
-        X86_FEATURE_XEN_IBRS_SET,                                       \
-        __stringify(DO_SPEC_CTRL_ENTRY maybexen=1 ibrs_val=0),          \
-        X86_FEATURE_XEN_IBRS_CLEAR
+    ALTERNATIVE __stringify(ASM_NOP39),                                 \
+        __stringify(DO_SPEC_CTRL_ENTRY maybexen=1), X86_FEATURE_SC_MSR
 
 /* Use when exiting to Xen context. */
 #define SPEC_CTRL_EXIT_TO_XEN                                           \
-    ALTERNATIVE_2 __stringify(ASM_NOP23),                               \
-        DO_SPEC_CTRL_EXIT_TO_XEN, X86_FEATURE_XEN_IBRS_SET,             \
-        DO_SPEC_CTRL_EXIT_TO_XEN, X86_FEATURE_XEN_IBRS_CLEAR
+    ALTERNATIVE __stringify(ASM_NOP23),                                 \
+        DO_SPEC_CTRL_EXIT_TO_XEN, X86_FEATURE_SC_MSR
 
 /* Use when exiting to guest context. */
 #define SPEC_CTRL_EXIT_TO_GUEST                                         \
-    ALTERNATIVE_2 __stringify(ASM_NOP24),                               \
-        DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_XEN_IBRS_SET,           \
-        DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_XEN_IBRS_CLEAR
+    ALTERNATIVE __stringify(ASM_NOP24),                                 \
+        DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_SC_MSR
 
 /* TODO: Drop these when the alternatives infrastructure is NMI/#MC safe. */
 .macro SPEC_CTRL_ENTRY_FROM_INTR_IST
