Re: [PATCH 3/4] x86/ftrace: make ftrace_int3_handler() not to skip fops invocation

[Andy Lutomirski]

On Mon, Apr 29, 2019 at 12:13 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
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> On Mon, Apr 29, 2019, 12:02 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
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>> If nmi were to break it, it would be a cpu bug.
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> Side note: we *already* depend on sti shadow working in other parts of the kernel, namely sti->iret.
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Where?  STI; IRET would be nuts.

Before:

commit 4214a16b02971c60960afd675d03544e109e0d75
Author: Andy Lutomirski <luto@xxxxxxxxxx>
Date:   Thu Apr 2 17:12:12 2015 -0700

    x86/asm/entry/64/compat: Use SYSRETL to return from compat mode SYSENTER

we did sti; sysxit, but, when we discussed this, I don't recall anyone
speaking up in favor of the safely of the old code.

Not to mention that the crash we'll get if we get an NMI and a
rescheduling interrupt in this path will be very, very hard to debug.