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Peter Anvin" , Alexey Makhalov , Ajay Kaher , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen Subject: [PATCH RESEND 2/2] x86/paravirt: Use XOR r32,r32 to clear register in pv_vcpu_is_preempted() Date: Wed, 14 Jan 2026 22:18:15 +0100 Message-ID: <20260114211948.74774-2-ubizjak@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260114211948.74774-1-ubizjak@gmail.com> References: <20260114211948.74774-1-ubizjak@gmail.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Juergen Gross Acked-by: "H. Peter Anvin" Acked-by: Alexey Makhalov Cc: Ajay Kaher Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen --- arch/x86/include/asm/paravirt-spinlock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/include/asm/paravirt-spinlock.h b/arch/x86/include/asm/paravirt-spinlock.h index 458b888aba84..7beffcb08ed6 100644 --- a/arch/x86/include/asm/paravirt-spinlock.h +++ b/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)); } -- 2.52.0