linux-kernel - Re: [PATCH] x86/vmware: use unsigned integer for shifting

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Message-ID: <53809b87-9b39-0aa9-dbc9-d5b40b3b46a6@gmail.com>
Date:   Fri, 20 May 2022 17:12:57 +0530
From:   Shreenidhi Shedi <yesshedi@...il.com>
To:     "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>,
        Borislav Petkov <bp@...en8.de>
Cc:     amakhalov@...are.com, tglx@...utronix.de, mingo@...hat.com,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        virtualization@...ts.linux-foundation.org, pv-drivers@...are.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Shreenidhi Shedi <sshedi@...are.com>
Subject: Re: [PATCH] x86/vmware: use unsigned integer for shifting

On 20/05/22 4:59 pm, Srivatsa S. Bhat wrote:
> Hi Shreenidhi,
> 
> Thank you for the patch!
> 
> On 5/20/22 2:26 AM, Borislav Petkov wrote:
>> On Fri, May 20, 2022 at 12:58:57PM +0530, Shreenidhi Shedi wrote:
>>> Shifting signed 32-bit value by 31 bits is implementation-defined
>>> behaviour. Using unsigned is better option for this.
>>>
> 
> Can you also add a "Fixes:" tag with the commit that introduced the
> issue? I believe it is 4cca6ea04d31 ("x86/apic: Allow x2apic without
> IR on VMware platform").
> 
>>> Signed-off-by: Shreenidhi Shedi <sshedi@...are.com>
>>> ---
>>>  arch/x86/kernel/cpu/vmware.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
>>> index c04b933f48d3..b28f789d3c56 100644
>>> --- a/arch/x86/kernel/cpu/vmware.c
>>> +++ b/arch/x86/kernel/cpu/vmware.c
>>> @@ -476,7 +476,7 @@ static bool __init vmware_legacy_x2apic_available(void)
>>>  {
>>>  	uint32_t eax, ebx, ecx, edx;
>>>  	VMWARE_CMD(GETVCPU_INFO, eax, ebx, ecx, edx);
>>> -	return (eax & (1 << VMWARE_CMD_VCPU_RESERVED)) == 0 &&
>>> +	return (eax & (1U << VMWARE_CMD_VCPU_RESERVED)) == 0 &&
>>>  	       (eax & (1 << VMWARE_CMD_LEGACY_X2APIC)) != 0;
>>
>> Or you can use the BIT() macro and simplify this expression even more:
>>
>>        return !(eax & BIT(VMWARE_CMD_VCPU_RESERVED)) &&
>>                (eax & BIT(VMWARE_CMD_LEGACY_X2APIC));
>>
>>
> 
> That's better indeed.
> 
> Regards,
> Srivatsa


Thanks for the quick reviews Boris and Srivatsa. I will make the changes and push the another patch soon.

--
Shedi