From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] kvm/x86 : avoid shifting signed 32-bit value by 31 bits Date: Mon, 15 Oct 2018 19:12:30 +0200 Message-ID: References: <20181006070849.psgrrhiysnrytbjr@master> <201810080904344038939@zte.com.cn> <20181008022532.4ve2xww4yphk6f5d@master> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: penghao122@sina.com.cn, 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: Wei Yang , peng.hao2@zte.com.cn Return-path: In-Reply-To: <20181008022532.4ve2xww4yphk6f5d@master> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 08/10/2018 04:25, Wei Yang wrote: > 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. I agree. Paolo