[v2] x86/vmware: use unsigned integer for shifting

[PATCH v2] x86/vmware: use unsigned integer for shifting

Posted by Shreenidhi Shedi 1 year, 11 months ago

From: Shreenidhi Shedi <yesshedi@gmail.com>

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")

Signed-off-by: Shreenidhi Shedi <sshedi@vmware.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))
 }
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
-- 
2.36.1

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

Posted by Thomas Gleixner 1 year, 11 months ago

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

> From: Shreenidhi Shedi <yesshedi@gmail.com>
>
> From: Shreenidhi Shedi <sshedi@vmware.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@vmware.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

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

Posted by Srivatsa S. Bhat 1 year, 11 months ago

On 5/20/22 7:09 AM, Shreenidhi Shedi wrote:
> From: Shreenidhi Shedi <yesshedi@gmail.com>
> 
> 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")
> 
> Signed-off-by: Shreenidhi Shedi <sshedi@vmware.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