On Tue, 22 Sep 2015, Dave Hansen wrote:
> On 09/22/2015 01:03 PM, Thomas Gleixner wrote:
> > On Wed, 16 Sep 2015, Dave Hansen wrote:
> >>
> >> +static inline u16 vma_pkey(struct vm_area_struct *vma)
> >> +{
> >> + u16 pkey = 0;
> >> +#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> >> + unsigned long f = vma->vm_flags;
> >> + pkey |= (!!(f & VM_HIGH_ARCH_0)) << 0;
> >> + pkey |= (!!(f & VM_HIGH_ARCH_1)) << 1;
> >> + pkey |= (!!(f & VM_HIGH_ARCH_2)) << 2;
> >> + pkey |= (!!(f & VM_HIGH_ARCH_3)) << 3;
> >
> > Eew. What's wrong with:
> >
> > pkey = (vma->vm_flags & VM_PKEY_MASK) >> VM_PKEY_SHIFT;
>
> I didn't do that only because we don't have any other need for
> VM_PKEY_MASK or VM_PKEY_SHIFT. We could do:
>
> #define VM_PKEY_MASK (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2...)
>
> static inline u16 vma_pkey(struct vm_area_struct *vma)
> {
> int vm_pkey_shift = __ffs(VM_PKEY_MASK)
> return (vma->vm_flags & VM_PKEY_MASK) >> vm_pkey_shift;
> }
>
> That's probably the same number of lines of code in the end. The
> compiler _probably_ ends up doing the same thing either way.
>
> >> +static u16 fetch_pkey(unsigned long address, struct task_struct *tsk)
> >
> > So here we get a u16 and assign it to si_pkey
> >
> >> + if (boot_cpu_has(X86_FEATURE_OSPKE) && si_code == SEGV_PKUERR)
> >> + info.si_pkey = fetch_pkey(address, tsk);
> >
> > which is int.
> >
> >> + int _pkey; /* FIXME: protection key value??
> >
> > Inconsistent at least.
>
> So I defined all the kernel-internal types as u16 since I *know* the
> size of the hardware.
>
> The user-exposed ones should probably be a bit more generic. I did just
> realize that this is an int and my proposed syscall is a long. That I
> definitely need to make consistent.
>
> Does anybody care whether it's an int or a long?
long is frowned upon due to 32/64bit. Even if that key stuff is only
available on 64bit for now ....
Thanks,
tglx
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>