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

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Message-ID: <Yode3m6iia9ZBHsl@zn.tnic>
Date:   Fri, 20 May 2022 11:26:54 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Shreenidhi Shedi <yesshedi@...il.com>
Cc:     srivatsa@...il.mit.edu, 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 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@...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));


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette