From: Shreenidhi Shedi <[email protected]>
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")
Cc: [email protected]
Signed-off-by: Shreenidhi Shedi <[email protected]>
---
arch/x86/kernel/cpu/vmware.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index c04b933f4..02039ec35 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -476,8 +476,8 @@ 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));
}
#ifdef CONFIG_AMD_MEM_ENCRYPT
--
2.36.1
On Fri, May 27, 2022 at 11:27:37PM +0530, Shreenidhi Shedi wrote:
> From: Shreenidhi Shedi <[email protected]>
>
> Shifting signed 32-bit value by 31 bits is implementation-defined
> behaviour. Using unsigned is better option for this.
The kernel builds with -fno-strict-overflow and as such this behaviour
is well defined.
> Fixes: 4cca6ea04d31 ("x86/apic: Allow x2apic without IR on VMware platform")
Nothing broken, therefore nothing fixed.
On 5/28/22 6:52 AM, Peter Zijlstra wrote:
> On Fri, May 27, 2022 at 11:27:37PM +0530, Shreenidhi Shedi wrote:
>> From: Shreenidhi Shedi <[email protected]>
>>
>> Shifting signed 32-bit value by 31 bits is implementation-defined
>> behaviour. Using unsigned is better option for this.
>
> The kernel builds with -fno-strict-overflow and as such this behaviour
> is well defined.
>
Ah, I see. Thank you, Peter!
>> Fixes: 4cca6ea04d31 ("x86/apic: Allow x2apic without IR on VMware platform")
>
> Nothing broken, therefore nothing fixed.
>
Agreed.
I think using the BIT() macro still provides a nice readability
improvement. So, Shreenidhi, could you spin a new version of the patch
with the same code changes but with a different commit message about
using the BIT() macro to simplify the code, and also include a
clarification as to why the existing code is correct (which Peter
pointed out), please?
Thank you!
Regards,
Srivatsa
VMware Photon OS