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>
Release-acked-by: Juergen Gross <jgross@suse.com>

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 1ad3ff594d2ea6ef249be80cc377e2deb77f47de..13e426cc95ef87b87e7edbdf2d0a69dad0b9805f 100644 (file)
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -128,8 +128,9 @@ static void __init print_details(enum ind_thunk thunk, uint64_t caps)
            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" : "");
@@ -366,13 +367,10 @@ void __init init_speculation_mitigations(void)
          * need the IBRS entry/exit logic to virtualise IBRS support for
          * guests.
          */
+        setup_force_cpu_cap(X86_FEATURE_SC_MSR);
+
         if ( ibrs )
-        {
             default_xen_spec_ctrl |= SPEC_CTRL_IBRS;
-            setup_force_cpu_cap(X86_FEATURE_XEN_IBRS_SET);
-        }
-        else
-            setup_force_cpu_cap(X86_FEATURE_XEN_IBRS_CLEAR);
 
         default_spec_ctrl_flags |= SCF_ist_wrmsr;
     }

diff --git a/xen/include/asm-x86/cpufeatures.h b/xen/include/asm-x86/cpufeatures.h
index c9b1a48807155983b960439a9d46274642b67523..ca58b0e88b6302e82179b89ceb1546c79204de81 100644 (file)
--- a/xen/include/asm-x86/cpufeatures.h
+++ b/xen/include/asm-x86/cpufeatures.h
@@ -26,8 +26,7 @@ XEN_CPUFEATURE(LFENCE_DISPATCH, (FSCAPINTS+0)*32+12) /* lfence set as Dispatch S
 XEN_CPUFEATURE(IND_THUNK_LFENCE,(FSCAPINTS+0)*32+13) /* Use IND_THUNK_LFENCE */
 XEN_CPUFEATURE(IND_THUNK_JMP,   (FSCAPINTS+0)*32+14) /* Use IND_THUNK_JMP */
 XEN_CPUFEATURE(XEN_IBPB,        (FSCAPINTS+0)*32+15) /* IBRSB || IBPB */
-XEN_CPUFEATURE(XEN_IBRS_SET,    (FSCAPINTS+0)*32+16) /* IBRSB && IRBS set in Xen */
-XEN_CPUFEATURE(XEN_IBRS_CLEAR,  (FSCAPINTS+0)*32+17) /* IBRSB && IBRS clear in Xen */
+XEN_CPUFEATURE(SC_MSR,          (FSCAPINTS+0)*32+16) /* MSR_SPEC_CTRL used by Xen */
 XEN_CPUFEATURE(RSB_NATIVE,      (FSCAPINTS+0)*32+18) /* RSB overwrite needed for native */
 XEN_CPUFEATURE(RSB_VMEXIT,      (FSCAPINTS+0)*32+19) /* RSB overwrite needed for vmexit */
 XEN_CPUFEATURE(NO_XPTI,         (FSCAPINTS+0)*32+20) /* XPTI mitigation not in use */

diff --git a/xen/include/asm-x86/spec_ctrl.h b/xen/include/asm-x86/spec_ctrl.h
index d5bd4dfacdf036c46ddc2318ec54c1eca2bad981..86a3dfe9642c8a7276db532afcbbd93ae4ce91a2 100644 (file)
--- a/xen/include/asm-x86/spec_ctrl.h
+++ b/xen/include/asm-x86/spec_ctrl.h
@@ -56,14 +56,14 @@ static always_inline void spec_ctrl_enter_idle(struct cpu_info *info)
     barrier();
     info->spec_ctrl_flags |= SCF_use_shadow;
     barrier();
-    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_XEN_IBRS_SET)
+    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_SC_MSR)
                    :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "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
@@ -71,7 +71,7 @@ static always_inline void spec_ctrl_exit_idle(struct cpu_info *info)
      */
     info->spec_ctrl_flags &= ~SCF_use_shadow;
     barrier();
-    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_XEN_IBRS_SET)
+    asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_SC_MSR)
                    :: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
 }
 

diff --git a/xen/include/asm-x86/spec_ctrl_asm.h b/xen/include/asm-x86/spec_ctrl_asm.h
index 97da08b95bc12c989427623252ffbf857909699c..730c998d0aef5a575d695ad7642835727c45c5fc 100644 (file)
--- 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
@@ -138,11 +138,11 @@
     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)
@@ -167,12 +167,12 @@
         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
 
@@ -219,45 +219,30 @@
 /* Use after a VMEXIT from an HVM guest. */
 #define SPEC_CTRL_ENTRY_FROM_VMEXIT                                     \
     ALTERNATIVE "", DO_OVERWRITE_RSB, X86_FEATURE_RSB_VMEXIT;           \
-    ALTERNATIVE_2 "",                                                   \
-        __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 "", 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 "", DO_OVERWRITE_RSB, X86_FEATURE_RSB_NATIVE;           \
-    ALTERNATIVE_2 "",                                                   \
-        __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(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 "", DO_OVERWRITE_RSB, X86_FEATURE_RSB_NATIVE;           \
-    ALTERNATIVE_2 "",                                                   \
-        __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(DO_SPEC_CTRL_ENTRY maybexen=1),         \
+        X86_FEATURE_SC_MSR
 
 /* Use when exiting to Xen context. */
 #define SPEC_CTRL_EXIT_TO_XEN                                           \
-    ALTERNATIVE_2 "",                                                   \
-        DO_SPEC_CTRL_EXIT_TO_XEN, X86_FEATURE_XEN_IBRS_SET,             \
-        DO_SPEC_CTRL_EXIT_TO_XEN, X86_FEATURE_XEN_IBRS_CLEAR
+    ALTERNATIVE "",                                                     \
+        DO_SPEC_CTRL_EXIT_TO_XEN, X86_FEATURE_SC_MSR
 
 /* Use when exiting to guest context. */
 #define SPEC_CTRL_EXIT_TO_GUEST                                         \
-    ALTERNATIVE_2 "",                                                   \
-        DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_XEN_IBRS_SET,           \
-        DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_XEN_IBRS_CLEAR
+    ALTERNATIVE "",                                                     \
+        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