* [PATCH v3] x86/vmware: use unsigned integer for shifting
@ 2022-05-27 17:57 Shreenidhi Shedi
2022-05-28 13:52 ` Peter Zijlstra
0 siblings, 1 reply; 3+ messages in thread
From: Shreenidhi Shedi @ 2022-05-27 17:57 UTC (permalink / raw)
To: srivatsa, amakhalov, tglx, mingo, bp, dave.hansen, hpa
Cc: virtualization, pv-drivers, x86, linux-kernel, yesshedi, stable,
Shreenidhi Shedi
From: Shreenidhi Shedi <sshedi@vmware.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")
Cc: stable@vger.kernel.org
Signed-off-by: Shreenidhi Shedi <sshedi@vmware.com>
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v3] x86/vmware: use unsigned integer for shifting
2022-05-27 17:57 [PATCH v3] x86/vmware: use unsigned integer for shifting Shreenidhi Shedi
@ 2022-05-28 13:52 ` Peter Zijlstra
2022-05-31 12:51 ` Srivatsa S. Bhat
0 siblings, 1 reply; 3+ messages in thread
From: Peter Zijlstra @ 2022-05-28 13:52 UTC (permalink / raw)
To: Shreenidhi Shedi
Cc: srivatsa, amakhalov, tglx, mingo, bp, dave.hansen, hpa,
virtualization, pv-drivers, x86, linux-kernel, stable,
Shreenidhi Shedi
On Fri, May 27, 2022 at 11:27:37PM +0530, Shreenidhi Shedi wrote:
> From: Shreenidhi Shedi <sshedi@vmware.com>
>
> 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.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v3] x86/vmware: use unsigned integer for shifting
2022-05-28 13:52 ` Peter Zijlstra
@ 2022-05-31 12:51 ` Srivatsa S. Bhat
0 siblings, 0 replies; 3+ messages in thread
From: Srivatsa S. Bhat @ 2022-05-31 12:51 UTC (permalink / raw)
To: Peter Zijlstra, Shreenidhi Shedi
Cc: amakhalov, tglx, mingo, bp, dave.hansen, hpa, virtualization,
pv-drivers, x86, linux-kernel, stable, Shreenidhi Shedi
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 <sshedi@vmware.com>
>>
>> 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
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-05-27 17:57 [PATCH v3] x86/vmware: use unsigned integer for shifting Shreenidhi Shedi
2022-05-28 13:52 ` Peter Zijlstra
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