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

["H. Peter Anvin" <hpa@zytor.com>]

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

On November 8, 2017 8:34:45 AM PST, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>On Wed, Nov 8, 2017 at 8:14 AM, Denys Vlasenko <dvlasenk@redhat.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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