linux-kernel - RE: [RFCv2 00/10] Linear Address Masking enabling

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Message-ID: <8a47d0ee50b44520a6f26177e6fe7ec5@AcuMS.aculab.com>
Date:   Fri, 13 May 2022 11:28:00 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alexander Potapenko' <glider@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        "Andi Kleen" <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: RE: [RFCv2 00/10] Linear Address Masking enabling

...
> Once we have the possibility to store tags in the pointers, we don't
> need redzones for heap/stack objects anymore, which saves quite a bit
> of memory.

You still need redzones.
The high bits are ignored for actual memory accesses.

To do otherwise you'd need the high bits to be in the PTE,
copied to the TLB and finally get into the cache tag.

Then you'd have to use the correct tags for each page.

	David

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