linux-kernel - Re: [PATCH] x86/special_insn: reverse __force

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Message-ID: <1E3FD845-E71A-4518-A0BF-FAD31CBC3E28@vmware.com>
Date:   Wed, 2 Sep 2020 15:32:18 +0000
From:   Nadav Amit <namit@...are.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86 <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] x86/special_insn: reverse __force_order logic

> On Sep 2, 2020, at 5:54 AM, peterz@...radead.org wrote:
> 
> On Tue, Sep 01, 2020 at 09:18:57AM -0700, Nadav Amit wrote:
> 
>> Unless I misunderstand the logic, __force_order should also be used by
>> rdpkru() and wrpkru() which do not have dependency on __force_order. I
>> also did not understand why native_write_cr0() has R/W dependency on
>> __force_order, and why native_write_cr4() no longer has any dependency
>> on __force_order.
> 
> There was a fairly large thread about this thing here:
> 
>  https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20200527135329.1172644-1-arnd%40arndb.de&amp;data=02%7C01%7Cnamit%40vmware.com%7C387b68745a984454d50708d84f3f499c%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637346480527901622&amp;sdata=PR%2BCUy%2FYNKza6he78coaDR3x1G7BYuzFfS9SGfWZ9p8%3D&amp;reserved=0
> 
> I didn't keep up, but I think the general concensus was that it's
> indeed a bit naf.

Thanks for pointer. I did not see the discussion, and embarrassingly, I have
also never figured out how to reply on lkml emails without registering to
lkml.

Anyhow, indeed, the patch that Arvind provided seems to address this issue.