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SubjectRe: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border
On Tue, 14 Nov 2017, Kirill A. Shutemov wrote:
> On Tue, Nov 14, 2017 at 05:01:50PM +0100, Thomas Gleixner wrote:
> > +bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
> > +{
> > + if (TASK_SIZE - len < addr)
> > + return false;
> > +#if CONFIG_PGTABLE_LEVELS >= 5
> > + return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
>
> Is it micro optimization? I don't feel it necessary. It's not that hot
> codepath to care about few cycles. (And one more place to care about for
> boot-time switching.)
>
> If you think it's needed, maybe IS_ENABLED() instead?

You're right. It's can be unconditional, For page table levels < 5 its just
redundant as its covered by the TASK_SIZE check already.

Thanks,

tglx

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