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From:   Andy Lutomirski <luto@kernel.org>
Date:   Thu, 1 Oct 2020 15:09:33 -0700
Message-ID: <CALCETrXPXxGZBGOf_DnYogamnkp29u8EqY33zDZb-HD+fj9ugg@mail.gmail.com>
Subject: Re: [PATCH v2 8/9] x86: Convert mmu context ia32_compat into a proper
 flags field
To:     Gabriel Krisman Bertazi <krisman@collabora.com>
Cc:     Andrew Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Christoph Hellwig <hch@lst.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Robert Richter <rric@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>, kernel@collabora.com
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On Thu, Oct 1, 2020 at 1:59 PM Gabriel Krisman Bertazi
<krisman@collabora.com> wrote:
>
> The ia32_compat attribute is a weird thing.  It mirrors TIF_IA32 and
> TIF_X32 and is used only in two very unrelated places: (1) to decide if
> the vsyscall page is accessible (2) for uprobes to find whether the
> patched instruction is 32 or 64 bit.  In preparation to remove the TI
> flags, we want new values for ia32_compat, but given its odd semantics,
> I'd rather make it a real flags field that configures these specific
> behaviours.  So, set_personality_x64 can ask for the vsyscall page,
> which is not available in x32/ia32 and set_personality_ia32 can
> configure the uprobe code as needed.
>
> uprobe cannot rely on other methods like user_64bit_mode() to decide how
> to patch, so it needs some specific flag like this.

I like this quite a bit, but can you rename MM_CONTEXT_GATE_PAGE to
MM_CONTEXT_HAS_VSYSCALL?

--Andy