Messages in this thread | | | Date | Thu, 16 Jun 2022 12:00:57 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCHv3 OPTIONAL 8/8] x86/mm: Extend LAM to support to LAM_U48 |
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On Fri, Jun 10, 2022 at 05:35:27PM +0300, Kirill A. Shutemov wrote: > LAM_U48 allows to encode 15 bits of tags into address. > > LAM_U48 steals bits above 47-bit for tags and makes it impossible for > userspace to use full address space on 5-level paging machine. > > Make these features mutually exclusive: whichever gets enabled first > blocks the other one.
This patch is broken in that it doesn't fix untag_pointer()
*If* you really want to continue down this road; you'll need something like:
#define untagged_addr(mm, addr) ({ \ u64 __addr = (__force u64)(addr); \ s64 sign = (s64)__addr >> 63; \ __addr ^= sign; \ __addr &= (mm)->context.untag_mask[sign & 1]; \ __addr ^= sign; \ (__force __typeof__(addr))__addr; \ })
Which uses a different mask for kernel and user pointers.
Anyway, without this U48 patch on, the mask could be a constant, no need to keep this variable, we can unconditionally unmask U57.
Let me go reply to that other mail too.
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