linux-kernel - RE: [PATCH] mm: Fix access_remote_vm() regression on tagged addresses

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Message-ID: <CY4PR11MB2005976F49613E20BC072ECCF913A@CY4PR11MB2005.namprd11.prod.outlook.com>
Date:   Thu, 10 Aug 2023 12:42:36 +0000
From:   "Schimpe, Christina" <christina.schimpe@...el.com>
To:     "Torvalds, Linus" <torvalds@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Kostya Serebryany <kcc@...gle.com>,
        "Andrey Ryabinin" <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH] mm: Fix access_remote_vm() regression on tagged addresses

> Interesting that it took this long to notice.
> 
> Not surprising considering that LAM isn't actually available, but I'd have
> expected the arm people to notice more. Yes, I have (and test) my
> arm64 laptop, but I obviously don't do user space debugging on it.
> Apparently others don't either.
> 
> Or maybe TBI is used a lot less than I thought.

Just for the record:

We don't have any LAM support in GDB yet, we are just working on it.
We currently rely on that feature, but could still change it. We don't 
necessarily require /proc/PID/mem to support tagged addresses.

ARM's TBI support in GDB does not rely on /proc/PID/mem to support tagged
addresses AFAIK.
I also thought that the kernel does not support tagged addresses for
/proc/PID/mem in case of ARM. This is at least reflected by their patches
for TBI and the kernel docs
https://www.kernel.org/doc/Documentation/arm64/tagged-pointers.txt.

Christina
Intel Deutschland GmbH
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