Messages in this thread | | | Date | Thu, 16 Jun 2022 12:02:16 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCHv3 5/8] x86/uaccess: Provide untagged_addr() and remove tags before address check |
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On Fri, Jun 10, 2022 at 05:35:24PM +0300, Kirill A. Shutemov wrote: > +#ifdef CONFIG_X86_64 > +/* > + * Mask out tag bits from the address. > + * > + * Magic with the 'sign' allows to untag userspace pointer without any branches > + * while leaving kernel addresses intact. > + */ > +#define untagged_addr(mm, addr) ({ \ > + u64 __addr = (__force u64)(addr); \ > + s64 sign = (s64)__addr >> 63; \ > + __addr ^= sign; \ > + __addr &= (mm)->context.untag_mask; \ > + __addr ^= sign; \ > + (__force __typeof__(addr))__addr; \ > +})
Can't we make that mask a constant and *always* unmask U57 irrespective of LAM being on?
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