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Peter Anvin" Subject: [PATCH RESEND 2/2] x86/paravirt: Use XOR r32,r32 to clear register in pv_vcpu_is_preempted() Date: Mon, 5 Jan 2026 10:39:07 +0100 Message-ID: <20260105093944.52387-2-ubizjak@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260105093944.52387-1-ubizjak@gmail.com> References: <20260105093944.52387-1-ubizjak@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: Ajay Kaher Cc: Alexey Makhalov Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" --- arch/x86/include/asm/paravirt.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h index 4f6ec60b4cb3..59aec695ae5f 100644 --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -577,7 +577,7 @@ static __always_inline void pv_kick(int cpu) static __always_inline bool pv_vcpu_is_preempted(long cpu) { return PVOP_ALT_CALLEE1(bool, lock.vcpu_is_preempted, cpu, - "xor %%" _ASM_AX ", %%" _ASM_AX, + "xor %%eax, %%eax", ALT_NOT(X86_FEATURE_VCPUPREEMPT)); } -- 2.52.0