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

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

[Borislav Petkov]

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.
> 
> Signed-off-by: Shreenidhi Shedi <sshedi@vmware.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));


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette
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Re: [PATCH] x86/vmware: use unsigned integer for shifting

[Srivatsa S. Bhat]

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@vmware.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
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