[PATCH -hyperv 1/3] x86/hyperv: Save segment registers directly to memory in hv_hvcrash_ctxt_save()

[Uros Bizjak]

hv_hvcrash_ctxt_save() in arch/x86/hyperv/hv_crash.c currently saves
segment registers via a general-purpose register (%eax). Update the
code to save segment registers (cs, ss, ds, es, fs, gs) directly to
the crash context memory using movw. This avoids unnecessary use of
a general-purpose register, making the code simpler and more efficient.

The size of the corresponding object file improves as follows:

   text    data     bss     dec     hex filename
   4167     176     200    4543    11bf hv_crash-old.o
   4151     176     200    4527    11af hv_crash-new.o

No functional change occurs to the saved context contents; this is
purely a code-quality improvement.

Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Wei Liu <wei.liu@xxxxxxxxxx>
Cc: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: Long Li <longli@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
---
 arch/x86/hyperv/hv_crash.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/hyperv/hv_crash.c b/arch/x86/hyperv/hv_crash.c
index fdb277bf73d8..2c7ea7e70854 100644
--- a/arch/x86/hyperv/hv_crash.c
+++ b/arch/x86/hyperv/hv_crash.c
@@ -207,12 +207,12 @@ static void hv_hvcrash_ctxt_save(void)
 	asm volatile("movq %%cr2, %0" : "=a"(ctxt->cr2));
 	asm volatile("movq %%cr8, %0" : "=a"(ctxt->cr8));
 
-	asm volatile("movl %%cs, %%eax" : "=a"(ctxt->cs));
-	asm volatile("movl %%ss, %%eax" : "=a"(ctxt->ss));
-	asm volatile("movl %%ds, %%eax" : "=a"(ctxt->ds));
-	asm volatile("movl %%es, %%eax" : "=a"(ctxt->es));
-	asm volatile("movl %%fs, %%eax" : "=a"(ctxt->fs));
-	asm volatile("movl %%gs, %%eax" : "=a"(ctxt->gs));
+	asm volatile("movw %%cs, %0" : "=m"(ctxt->cs));
+	asm volatile("movw %%ss, %0" : "=m"(ctxt->ss));
+	asm volatile("movw %%ds, %0" : "=m"(ctxt->ds));
+	asm volatile("movw %%es, %0" : "=m"(ctxt->es));
+	asm volatile("movw %%fs, %0" : "=m"(ctxt->fs));
+	asm volatile("movw %%gs, %0" : "=m"(ctxt->gs));
 
 	native_store_gdt(&ctxt->gdtr);
 	store_idt(&ctxt->idtr);
-- 
2.53.0