linux-kernel - Re: [PATCH v2] x86/vmware: use unsigned integer for shifting

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Message-ID: <87pmk7iy62.ffs@tglx>
Date:   Sat, 21 May 2022 01:25:57 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Shreenidhi Shedi <yesshedi@...il.com>, srivatsa@...il.mit.edu,
        amakhalov@...are.com, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com
Cc:     virtualization@...ts.linux-foundation.org, pv-drivers@...are.com,
        x86@...nel.org, linux-kernel@...r.kernel.org, yesshedi@...il.com,
        Shreenidhi Shedi <sshedi@...are.com>
Subject: Re: [PATCH v2] x86/vmware: use unsigned integer for shifting

On Fri, May 20 2022 at 19:39, Shreenidhi Shedi wrote:

> From: Shreenidhi Shedi <yesshedi@...il.com>
>
> From: Shreenidhi Shedi <sshedi@...are.com>

Can you please decide which of your personalities wrote that patch?

> Shifting signed 32-bit value by 31 bits is implementation-defined
> behaviour. Using unsigned is better option for this.

Better option? There are no options. It's either correct or not. Please
be precise and technical in your wording.

> Fixes: 4cca6ea04d31 ("x86/apic: Allow x2apic without IR on VMware platform")
>
> Signed-off-by: Shreenidhi Shedi <sshedi@...are.com>

Please keep the tags together. This extra new line is pointless and
makes the maintainer do extra work to remove it.

Documentation/process/* has all the relevant directives for
you. Following them is not an option. It's mandatory.

> @@ -476,8 +477,8 @@ 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 &&
> -	       (eax & (1 << VMWARE_CMD_LEGACY_X2APIC)) != 0;
> +	return !(eax & BIT(VMWARE_CMD_VCPU_RESERVED)) &&
> +		(eax & BIT(VMWARE_CMD_LEGACY_X2APIC))

Testing your changes before submission is not optional either. How is
this supposed to compile?

Thanks,

        tglx