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Date: Sun, 28 Apr 2019 13:51:43 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Andy Lutomirski <luto@...capital.net> Cc: Nicolai Stange <nstange@...e.de>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, Josh Poimboeuf <jpoimboe@...hat.com>, Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>, Petr Mladek <pmladek@...e.com>, Joe Lawrence <joe.lawrence@...hat.com>, Shuah Khan <shuah@...nel.org>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Tim Chen <tim.c.chen@...ux.intel.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Mimi Zohar <zohar@...ux.ibm.com>, Juergen Gross <jgross@...e.com>, Nick Desaulniers <ndesaulniers@...gle.com>, Nayna Jain <nayna@...ux.ibm.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Andy Lutomirski <luto@...nel.org>, Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, linux-kselftest@...r.kernel.org Subject: Re: [PATCH 1/4] x86/thread_info: introduce ->ftrace_int3_stack member On Sun, 28 Apr 2019 10:41:10 -0700 Andy Lutomirski <luto@...capital.net> wrote: > > Note that at any given point > > in time, there can be at most four such call insn emulations pending: > > namely at most one per "process", "irq", "softirq" and "nmi" context. > > > > That’s quite an assumption. I think your list should also contain > exception, exceptions nested inside that exception, and machine > check, at the very least. I’m also wondering why irq and softirq are > treated separately. 4 has usually been the context count we choose. But I guess in theory, if we get exceptions then I could potentially be more. As for irq vs softirq, an interrupt can preempt a softirq. Interrupts are enabled while softirqs are running. When sofirqs run, softirqs are disabled to prevent nested softirqs. But interrupts are enabled again, and another interrupt may come in while a softirq is executing. > > All this makes me think that one of the other solutions we came up > with last time we discussed this might be better. +100 Perhaps adding another slot into pt_regs that gets used by int3 to store a slot to emulate a call on return? -- Steve
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