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

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Date:   Wed, 08 Nov 2017 08:38:18 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Denys Vlasenko <dvlasenk@...hat.com>
CC:     Paolo Bonzini <pbonzini@...hat.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"@zytor.com
Subject: Re: [tip:x86/asm] x86/umip: Add emulation code for UMIP instructions

<linux-tip-commits@...r.kernel.org>
From: hpa@...or.com
Message-ID: <67A3DB9F-E58D-42B3-BF16-AC59D2FCECC2@...or.com>

On November 8, 2017 8:34:45 AM PST, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>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

The real problem is that 16-bit software uses the instructions mostly for stupid reasons, but smsw in particular is used exactly because it is a virtualization hole.
-- 
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