* Re: [PATCH] kvm: vmx: Silence a shift wrap warning
2019-03-25 9:04 [PATCH] kvm: vmx: Silence a shift wrap warning Dan Carpenter
@ 2019-03-25 9:29 ` David Hildenbrand
2019-03-26 7:07 ` Dan Carpenter
2019-03-26 8:10 ` David Hildenbrand
2 siblings, 0 replies; 4+ messages in thread
From: David Hildenbrand @ 2019-03-25 9:29 UTC (permalink / raw)
To: kernel-janitors
On 25.03.19 10:04, Dan Carpenter wrote:
> This code generates a Smatch warning:
>
> arch/x86/kvm/vmx/nested.c:4828 handle_vmfunc() warn: should '(1 << function)' be a 64 bit type?
>
> The warning is generated because "vmcs12->vm_function_control" is a u64
> but the shift can only test the lower 32 bits. This doesn't cause a
> problem in the current code because we only use BIT(0). This patch just
> silences the static checker warning.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> arch/x86/kvm/vmx/nested.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index f24a2c225070..1f4398246bd9 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4825,7 +4825,7 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
> }
>
> vmcs12 = get_vmcs12(vcpu);
> - if ((vmcs12->vm_function_control & (1 << function)) = 0)
> + if ((vmcs12->vm_function_control & (1ULL << function)) = 0)
I guess one set of parentheses could be dropped here, while touching the
line.
Reviewed-by: David Hildenbrand <david@redhat.com>
> goto fail;
>
> switch (function) {
>
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] kvm: vmx: Silence a shift wrap warning
2019-03-25 9:04 [PATCH] kvm: vmx: Silence a shift wrap warning Dan Carpenter
2019-03-25 9:29 ` David Hildenbrand
@ 2019-03-26 7:07 ` Dan Carpenter
2019-03-26 8:10 ` David Hildenbrand
2 siblings, 0 replies; 4+ messages in thread
From: Dan Carpenter @ 2019-03-26 7:07 UTC (permalink / raw)
To: kernel-janitors
On Mon, Mar 25, 2019 at 10:29:40AM +0100, David Hildenbrand wrote:
> On 25.03.19 10:04, Dan Carpenter wrote:
> > This code generates a Smatch warning:
> >
> > arch/x86/kvm/vmx/nested.c:4828 handle_vmfunc() warn: should '(1 << function)' be a 64 bit type?
> >
> > The warning is generated because "vmcs12->vm_function_control" is a u64
> > but the shift can only test the lower 32 bits. This doesn't cause a
> > problem in the current code because we only use BIT(0). This patch just
> > silences the static checker warning.
> >
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > arch/x86/kvm/vmx/nested.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index f24a2c225070..1f4398246bd9 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -4825,7 +4825,7 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
> > }
> >
> > vmcs12 = get_vmcs12(vcpu);
> > - if ((vmcs12->vm_function_control & (1 << function)) = 0)
> > + if ((vmcs12->vm_function_control & (1ULL << function)) = 0)
>
> I guess one set of parentheses could be dropped here, while touching the
> line.
The problem is bitwise AND has low precedence so the parenthesis are
either required or they improve readability. You could write it like
this:
if ((vmcs12->vm_function_control & 1ULL << function) = 0)
but no one does.
>
> Reviewed-by: David Hildenbrand <david@redhat.com>
>
Thanks!
regards,
dan carpenter
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] kvm: vmx: Silence a shift wrap warning
2019-03-25 9:04 [PATCH] kvm: vmx: Silence a shift wrap warning Dan Carpenter
2019-03-25 9:29 ` David Hildenbrand
2019-03-26 7:07 ` Dan Carpenter
@ 2019-03-26 8:10 ` David Hildenbrand
2 siblings, 0 replies; 4+ messages in thread
From: David Hildenbrand @ 2019-03-26 8:10 UTC (permalink / raw)
To: kernel-janitors
On 26.03.19 08:07, Dan Carpenter wrote:
> On Mon, Mar 25, 2019 at 10:29:40AM +0100, David Hildenbrand wrote:
>> On 25.03.19 10:04, Dan Carpenter wrote:
>>> This code generates a Smatch warning:
>>>
>>> arch/x86/kvm/vmx/nested.c:4828 handle_vmfunc() warn: should '(1 << function)' be a 64 bit type?
>>>
>>> The warning is generated because "vmcs12->vm_function_control" is a u64
>>> but the shift can only test the lower 32 bits. This doesn't cause a
>>> problem in the current code because we only use BIT(0). This patch just
>>> silences the static checker warning.
>>>
>>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>>> ---
>>> arch/x86/kvm/vmx/nested.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>>> index f24a2c225070..1f4398246bd9 100644
>>> --- a/arch/x86/kvm/vmx/nested.c
>>> +++ b/arch/x86/kvm/vmx/nested.c
>>> @@ -4825,7 +4825,7 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
>>> }
>>>
>>> vmcs12 = get_vmcs12(vcpu);
>>> - if ((vmcs12->vm_function_control & (1 << function)) = 0)
>>> + if ((vmcs12->vm_function_control & (1ULL << function)) = 0)
>>
>> I guess one set of parentheses could be dropped here, while touching the
>> line.
>
> The problem is bitwise AND has low precedence so the parenthesis are
> either required or they improve readability. You could write it like
> this:
>
> if ((vmcs12->vm_function_control & 1ULL << function) = 0)
>
> but no one does.
Yes, you're right, my intuition was wrong this time :)
Cheers!
>
>>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>>
>
> Thanks!
>
> regards,
> dan carpenter
>
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 4+ messages in thread