linux-kernel - Re: [PATCHv3 0/8] Linear Address Masking enabling

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Date:   Thu, 16 Jun 2022 23:48:47 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "andreyknvl@...il.com" <andreyknvl@...il.com>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "ryabinin.a.a@...il.com" <ryabinin.a.a@...il.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "glider@...gle.com" <glider@...gle.com>
Subject: Re: [PATCHv3 0/8] Linear Address Masking enabling

On Fri, 2022-06-17 at 02:43 +0300, Kirill A. Shutemov wrote:
> On Thu, Jun 16, 2022 at 10:52:14PM +0000, Edgecombe, Rick P wrote:
> > On Fri, 2022-06-10 at 17:35 +0300, Kirill A. Shutemov wrote:
> > > Linear Address Masking[1] (LAM) modifies the checking that is
> > > applied
> > > to
> > > 64-bit linear addresses, allowing software to use of the
> > > untranslated
> > > address bits for metadata.
> > > 
> > > The patchset brings support for LAM for userspace addresses.
> > 
> > Arm has this documentation about which memory operations support
> > being
> > passed tagged pointers, and which do not:
> > Documentation/arm64/tagged-address-abi.rst
> > 
> > Is the idea that LAM would have something similar, or exactly
> > mirror
> > the arm ABI? It seems like it is the same right now. Should the
> > docs be
> > generalized?
> 
> It is somewhat similar, but not exact. ARM TBI interface implies tag
> size
> and placement. ARM TBI is per-thread and LAM is per-process.

Ah right. I was thinking more the part about which syscalls support
tagged addresses:

https://www.kernel.org/doc/html/latest/arm64/tagged-address-abi.html#id1

Some mention kernel versions where they changed. Just thinking it could
get complex to track which HW features support which syscalls for which
kernel versions.