linux-kernel - Re: [PATCH v3 09/10] x86: Convert mmu context ia32

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Date:   Wed, 7 Oct 2020 17:07:37 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Robert Richter <rric@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        kernel@...labora.com
Subject: Re: [PATCH v3 09/10] x86: Convert mmu context ia32_compat into a
 proper flags field

On Sat, Oct 3, 2020 at 8:26 PM Gabriel Krisman Bertazi
<krisman@...labora.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.

Acked-by: Andy Lutomirski<luto@...nel.org>

There are still issues with vsyscall control, but they were
pre-existing and I'll try to get them fixed up.

--Andy