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

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Message-ID: <a38ef828-dbfa-59c0-475d-e16c44267e6b@csail.mit.edu>
Date:   Fri, 20 May 2022 17:41:18 +0200
From:   "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
To:     Shreenidhi Shedi <yesshedi@...il.com>, amakhalov@...are.com,
        tglx@...utronix.de, 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,
        Shreenidhi Shedi <sshedi@...are.com>
Subject: Re: [PATCH v2] x86/vmware: use unsigned integer for shifting

On 5/20/22 7:09 AM, Shreenidhi Shedi wrote:
> From: Shreenidhi Shedi <yesshedi@...il.com>
> 
> From: Shreenidhi Shedi <sshedi@...are.com>
> 
> Shifting signed 32-bit value by 31 bits is implementation-defined
> behaviour. Using unsigned is better option for this.
> 
> Fixes: 4cca6ea04d31 ("x86/apic: Allow x2apic without IR on VMware platform")
> 
> Signed-off-by: Shreenidhi Shedi <sshedi@...are.com>
> ---
>  arch/x86/kernel/cpu/vmware.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> index c04b933f48d3..cd809c5b17f0 100644
> --- a/arch/x86/kernel/cpu/vmware.c
> +++ b/arch/x86/kernel/cpu/vmware.c
> @@ -28,6 +28,7 @@
>  #include <linux/cpu.h>
>  #include <linux/reboot.h>
>  #include <linux/static_call.h>
> +#include <linux/bits.h>
>  #include <asm/div64.h>
>  #include <asm/x86_init.h>
>  #include <asm/hypervisor.h>
> @@ -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))


This patch has clearly not been tested, and not even compiled! (It is
missing a semicolon at the end of the return statement).

Please take your time to revise and test your patch based on the
review feedback; there is no hurry! :)

(Also, while at it, the double From: at the beginning of the patch
needs to be fixed too).

Regards,
Srivatsa