[Xen-changelog] [xen master] x86/traps: don't use 16bit reads of segment registers

[patchbot@xxxxxxx]

commit ee653b97ce369decfdd4d18979fd9f6aec0073c2
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Oct 14 12:48:36 2015 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Oct 14 12:48:36 2015 +0200

    x86/traps: don't use 16bit reads of segment registers
    
    When executing `mov %sreg, %r32`, older Intel processors would leave the
    upper 16 bits of %r32 undefined.  P4 processors and newer, as well as
    all AMD processors will zero extend the segment selector.
    
    As Xen only supports 64bit these days, there is no need to use the
    operand-size override prefix and suffer the resulting pipeline overhead.
    
    Rename read_segment_register() to read_sreg() and drop the existing
    read_sreg() wrapper which took a regs parameter and did nothing with it.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/domain.c        |    8 ++++----
 xen/arch/x86/traps.c         |   26 ++++++++++++--------------
 xen/arch/x86/x86_64/traps.c  |   16 ++++++++--------
 xen/include/asm-x86/system.h |    6 +++---
 4 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 91c04f8..fe3be30 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1412,10 +1412,10 @@ static void save_segments(struct vcpu *v)
     struct cpu_user_regs *regs = &v->arch.user_regs;
     unsigned int dirty_segment_mask = 0;
 
-    regs->ds = read_segment_register(ds);
-    regs->es = read_segment_register(es);
-    regs->fs = read_segment_register(fs);
-    regs->gs = read_segment_register(gs);
+    regs->ds = read_sreg(ds);
+    regs->es = read_sreg(es);
+    regs->fs = read_sreg(fs);
+    regs->gs = read_sreg(gs);
 
     if ( cpu_has_fsgsbase && !is_pv_32bit_vcpu(v) )
     {
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index f1fc7b7..8093535 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1981,8 +1981,6 @@ static inline uint64_t guest_misc_enable(uint64_t val)
     }                                                                       \
     (eip) += sizeof(_x); _x; })
 
-#define read_sreg(regs, sr) read_segment_register(sr)
-
 static int is_cpufreq_controller(struct domain *d)
 {
     return ((cpufreq_controller == FREQCTL_dom0_kernel) &&
@@ -2029,7 +2027,7 @@ static int emulate_privileged_op(struct cpu_user_regs 
*regs)
         goto fail;
 
     /* emulating only opcodes not allowing SS to be default */
-    data_sel = read_sreg(regs, ds);
+    data_sel = read_sreg(ds);
 
     /* Legacy prefixes. */
     for ( i = 0; i < 8; i++, rex == opcode || (rex = 0) )
@@ -2047,17 +2045,17 @@ static int emulate_privileged_op(struct cpu_user_regs 
*regs)
             data_sel = regs->cs;
             continue;
         case 0x3e: /* DS override */
-            data_sel = read_sreg(regs, ds);
+            data_sel = read_sreg(ds);
             continue;
         case 0x26: /* ES override */
-            data_sel = read_sreg(regs, es);
+            data_sel = read_sreg(es);
             continue;
         case 0x64: /* FS override */
-            data_sel = read_sreg(regs, fs);
+            data_sel = read_sreg(fs);
             lm_ovr = lm_seg_fs;
             continue;
         case 0x65: /* GS override */
-            data_sel = read_sreg(regs, gs);
+            data_sel = read_sreg(gs);
             lm_ovr = lm_seg_gs;
             continue;
         case 0x36: /* SS override */
@@ -2104,7 +2102,7 @@ static int emulate_privileged_op(struct cpu_user_regs 
*regs)
 
         if ( !(opcode & 2) )
         {
-            data_sel = read_sreg(regs, es);
+            data_sel = read_sreg(es);
             lm_ovr = lm_seg_none;
         }
 
@@ -2912,22 +2910,22 @@ static void emulate_gate_op(struct cpu_user_regs *regs)
             ASSERT(opnd_sel);
             continue;
         case 0x3e: /* DS override */
-            opnd_sel = read_sreg(regs, ds);
+            opnd_sel = read_sreg(ds);
             if ( !opnd_sel )
                 opnd_sel = dpl;
             continue;
         case 0x26: /* ES override */
-            opnd_sel = read_sreg(regs, es);
+            opnd_sel = read_sreg(es);
             if ( !opnd_sel )
                 opnd_sel = dpl;
             continue;
         case 0x64: /* FS override */
-            opnd_sel = read_sreg(regs, fs);
+            opnd_sel = read_sreg(fs);
             if ( !opnd_sel )
                 opnd_sel = dpl;
             continue;
         case 0x65: /* GS override */
-            opnd_sel = read_sreg(regs, gs);
+            opnd_sel = read_sreg(gs);
             if ( !opnd_sel )
                 opnd_sel = dpl;
             continue;
@@ -2980,7 +2978,7 @@ static void emulate_gate_op(struct cpu_user_regs *regs)
                             switch ( modrm & 7 )
                             {
                             default:
-                                opnd_sel = read_sreg(regs, ds);
+                                opnd_sel = read_sreg(ds);
                                 break;
                             case 4: case 5:
                                 opnd_sel = regs->ss;
@@ -3008,7 +3006,7 @@ static void emulate_gate_op(struct cpu_user_regs *regs)
                             break;
                         }
                         if ( !opnd_sel )
-                            opnd_sel = read_sreg(regs, ds);
+                            opnd_sel = read_sreg(ds);
                         switch ( modrm & 7 )
                         {
                         case 0: case 2: case 4:
diff --git a/xen/arch/x86/x86_64/traps.c b/xen/arch/x86/x86_64/traps.c
index 0846a19..b7c2759 100644
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -125,10 +125,10 @@ void show_registers(const struct cpu_user_regs *regs)
         fault_crs[0] = read_cr0();
         fault_crs[3] = read_cr3();
         fault_crs[4] = read_cr4();
-        fault_regs.ds = read_segment_register(ds);
-        fault_regs.es = read_segment_register(es);
-        fault_regs.fs = read_segment_register(fs);
-        fault_regs.gs = read_segment_register(gs);
+        fault_regs.ds = read_sreg(ds);
+        fault_regs.es = read_sreg(es);
+        fault_regs.fs = read_sreg(fs);
+        fault_regs.gs = read_sreg(gs);
     }
 
     print_xen_info();
@@ -242,10 +242,10 @@ void do_double_fault(struct cpu_user_regs *regs)
     crs[2] = read_cr2();
     crs[3] = read_cr3();
     crs[4] = read_cr4();
-    regs->ds = read_segment_register(ds);
-    regs->es = read_segment_register(es);
-    regs->fs = read_segment_register(fs);
-    regs->gs = read_segment_register(gs);
+    regs->ds = read_sreg(ds);
+    regs->es = read_sreg(es);
+    regs->fs = read_sreg(fs);
+    regs->gs = read_sreg(gs);
 
     printk("CPU:    %d\n", cpu);
     _show_registers(regs, crs, CTXT_hypervisor, NULL);
diff --git a/xen/include/asm-x86/system.h b/xen/include/asm-x86/system.h
index 9fb70f5..eb498f5 100644
--- a/xen/include/asm-x86/system.h
+++ b/xen/include/asm-x86/system.h
@@ -5,9 +5,9 @@
 #include <xen/bitops.h>
 #include <asm/processor.h>
 
-#define read_segment_register(name)                             \
-({  u16 __sel;                                                  \
-    asm volatile ( "movw %%" STR(name) ",%0" : "=r" (__sel) );  \
+#define read_sreg(name)                                         \
+({  unsigned int __sel;                                         \
+    asm volatile ( "mov %%" STR(name) ",%0" : "=r" (__sel) );   \
     __sel;                                                      \
 })
 
--
generated by git-patchbot for /home/xen/git/xen.git#master

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