2022-05-22 09:03:58

by Borislav Petkov

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 <[email protected]>
> ---
> 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

2022-05-23 06:30:53

by Srivatsa S. Bhat

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

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 <[email protected]>
>> ---
>> 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