From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Yang Subject: Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits Date: Mon, 8 Oct 2018 02:25:32 +0000 Message-ID: <20181008022532.4ve2xww4yphk6f5d@master> References: <20181006070849.psgrrhiysnrytbjr@master> <201810080904344038939@zte.com.cn> Reply-To: Wei Yang Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: richard.weiyang@gmail.com, penghao122@sina.com.cn, pbonzini@redhat.com, rkrcmar@redhat.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, joro@8bytes.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org To: peng.hao2@zte.com.cn Return-path: Content-Disposition: inline In-Reply-To: <201810080904344038939@zte.com.cn> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, Oct 08, 2018 at 09:04:34AM +0800, peng.hao2@zte.com.cn wrote: >>On Sat, Oct 06, 2018 at 11:31:04AM +0800, peng.hao2@zte.com.cn wrote: >>>>On Thu, Oct 04, 2018 at 01:47:18PM -0400, Peng Hao wrote: >>>>> >>>>>From: Peng Hao >>>>> >>>>> modify AVIC_LOGICAL_ID_ENTRY_VALID_MASK to unsigned >>>>> >>>>>Signed-off-by: Peng Hao >>>>>--- >>>>> arch/x86/kvm/svm.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>>diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c >>>>>index d96092b..bf1ded4 100644 >>>>>--- a/arch/x86/kvm/svm.c >>>>>+++ b/arch/x86/kvm/svm.c >>>>>@@ -262,7 +262,7 @@ struct amd_svm_iommu_ir { >>>>> }; >>>>> >>>>> #define AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK (0xFF) >>>>>-#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK (1 << 31) >>>>>+#define AVIC_LOGICAL_ID_ENTRY_VALID_MASK (1UL << 31) >>> >>>>It is reasonable to change to unsigned, while not necessary to unsigned >>>>long? >>>AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used in function avic_ldr_write. >>>here I think it doesn't matter if you use unsigned or unsigned long. Do you have any suggestions? > >>In current case, AVIC_LOGICAL_ID_ENTRY_VALID_MASK is used to calculate >>the value of new_entry with type of u32. So the definition here is not >>harmful. > >>Also, I did a quick grep and found similar definition (1 << 31) is popular >>in the whole kernel tree. > >>The reason to make this change is not that strong to me. Would you >>minding sharing more reason behind this change? >oh, I'm just thinking logically, not more reason. This definition may introduce problem when this value is used to calculate a 64bit data. Since current entry is 32bit, we may leave it as it is for now. -- Wei Yang Help you, Help me