x86/hyperv: Use any general-purpose register when saving %cr2 and %cr8

hv_hvcrash_ctxt_save() in arch/x86/hyperv/hv_crash.c currently saves %cr2
and %cr8 using %eax ("=a"). This unnecessarily forces a specific register.
Update the inline assembly to use a general-purpose register ("=r") for
both %cr2 and %cr8. This makes the code more flexible for the compiler
while producing the same saved context contents.

No functional changes.

Signed-off-by: Uros Bizjak <[email protected]>
Cc: K. Y. Srinivasan <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Wei Liu <[email protected]>
Cc: Dexuan Cui <[email protected]>
Cc: Long Li <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Signed-off-by: Wei Liu <[email protected]>

Author: ubizjak

arch/x86/hyperv/hv_crash.c

@@ -204,8 +204,8 @@ static void hv_hvcrash_ctxt_save(void)
 	ctxt->cr0 = native_read_cr0();
 	ctxt->cr4 = native_read_cr4();
 
-	asm volatile("movq %%cr2, %0" : "=a"(ctxt->cr2));
-	asm volatile("movq %%cr8, %0" : "=a"(ctxt->cr8));
+	asm volatile("movq %%cr2, %0" : "=r"(ctxt->cr2));
+	asm volatile("movq %%cr8, %0" : "=r"(ctxt->cr8));
 
 	asm volatile("movw %%cs, %0" : "=m"(ctxt->cs));
 	asm volatile("movw %%ss, %0" : "=m"(ctxt->ss));