linux-kernel - Re: [PATCHv3 3/8] mm: Pass down mm_struct to untagged

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Message-ID: <CAG_fn=Whre1PdfxoT=isho9auAQeBaH4ghU+orcJfgdeD30g3w@mail.gmail.com>
Date:   Fri, 17 Jun 2022 17:27:46 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        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: [PATCHv3 3/8] mm: Pass down mm_struct to untagged_addr()

On Fri, Jun 10, 2022 at 4:35 PM Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> Intel Linear Address Masking (LAM) brings per-mm untagging rules. Pass
> down mm_struct to the untagging helper. It will help to apply untagging
> policy correctly.
>
> In most cases, current->mm is the one to use, but there are some
> exceptions, such as get_user_page_remote().

Wouldn't it be easier to keep using current->mm in untagged_addr(addr)
by default, and introduce a separate macro for the exceptions?

>
> +/*
> + * Architectures that support memory tagging (assigning tags to memory regions,
> + * embedding these tags into addresses that point to these memory regions, and
> + * checking that the memory and the pointer tags match on memory accesses)
> + * redefine this macro to strip tags from pointers.
> + * It's defined as noop for architectures that don't support memory tagging.
> + */
> +#ifndef untagged_addr
> +#define untagged_addr(mm, addr) (addr)
> +#endif
The comment above should probably be extended to explain the effect of `mm`.




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Alexander Potapenko
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