linux-kernel - Re: [tip:x86/asm] x86/umip: Add emulation code for UMIP instructions

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Message-ID: <CA+55aFyzb5D6DfM_1mxcMbuYOaxZWFxqfv7WZS6zdkqnN7+p0A@mail.gmail.com>
Date:   Wed, 8 Nov 2017 08:34:45 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Denys Vlasenko <dvlasenk@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Anvin <hpa@...or.com>,
        Borislav Petkov <bp@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Jonathan Corbet <corbet@....net>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        ricardo.neri-calderon@...ux.intel.com,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>, ray.huang@....com,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Chen Yucong <slaoub@...il.com>, Ingo Molnar <mingo@...nel.org>,
        Jiri Slaby <jslaby@...e.cz>, Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/asm] x86/umip: Add emulation code for UMIP instructions

On Wed, Nov 8, 2017 at 8:14 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
>
> Can we avoid maintain emulation of these isns, by asking Wine to remove
> their use instead?

If we ask the Wine people to remove the instruction use, that may mean
that we can avoid the emulation in four or five _years_ once everybody
has updated.

But it wouldn't mean that we could avoid it today.

We *do* probably want to print a warning about these instructions,
whether emulated or not. If emulated, we want to print a warning about
the emulation being expensive (as a nudge to the Wine people to not do
that), and if _not_ emulated, we'd want to print a warning about why
people suddenly got a SIGSEGV in case there are programs that use
those instructions that people didn't even think of.

But make it ratelimit the warning (perhaps at most once every few
minutes or whatever), so that people won't flood message logs just
because they have old stupid programs that use those things.

             Linus