linux-kernel - Re: [PATCHv15 05/17] mm: Introduce untagged_addr

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Date:   Thu, 9 Feb 2023 15:08:53 +0100
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>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Taras Madan <tarasmadan@...gle.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>,
        Bharata B Rao <bharata@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv15 05/17] mm: Introduce untagged_addr_remote()

On Mon, Jan 23, 2023 at 11:05 PM Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> untagged_addr() removes tags/metadata from the address and brings it to
> the canonical form. The helper is implemented on arm64 and sparc. Both of
> them do untagging based on global rules.
>
> However, Linear Address Masking (LAM) on x86 introduces per-process
> settings for untagging. As a result, untagged_addr() is now only
> suitable for untagging addresses for the current proccess.
>
> The new helper untagged_addr_remote() has to be used when the address
> targets remote process. It requires the mmap lock for target mm to be
> taken.
>
> Export dump_mm() as there's now the first user for it: VFIO can be
> compiled as module and untagged_addr_remote() triggers dump_mm() via
> mmap_assert_locked().
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Alexander Potapenko <glider@...gle.com>