| Message ID | 20190325090448.GB16023@kadam (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kvm: vmx: Silence a shift wrap warning | expand |
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) { >
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
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 >
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) goto fail; switch (function) {
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(-)