x86/paravirt: Use XOR r32,r32 to clear register in pv_vcpu_is_preempted()

x86_64 zero extends 32bit operations, so for 64bit operands, XOR r32,r32 is
functionally equal to XOR r64,r64, but avoids a REX prefix byte when legacy
registers are used.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: Alexey Makhalov <alexey.makhalov@broadcom.com>
Link: https://patch.msgid.link/20260114211948.74774-2-ubizjak@gmail.com

Author: ubizjak

arch/x86/include/asm/paravirt-spinlock.h

@@ -45,7 +45,7 @@ static __always_inline void pv_queued_spin_unlock(struct qspinlock *lock)
 static __always_inline bool pv_vcpu_is_preempted(long cpu)
 {
 	return PVOP_ALT_CALLEE1(bool, pv_ops_lock, vcpu_is_preempted, cpu,
-				"xor %%" _ASM_AX ", %%" _ASM_AX,
+				"xor %%eax, %%eax",
 				ALT_NOT(X86_FEATURE_VCPUPREEMPT));
 }