linux-kernel - Re: [PATCH v5 22/34] x86/fred: FRED initialization code

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Date:   Mon, 20 Mar 2023 17:49:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>, Xin Li <xin3.li@...el.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, andrew.cooper3@...rix.com,
        seanjc@...gle.com, pbonzini@...hat.com, ravi.v.shankar@...el.com
Subject: Re: [PATCH v5 22/34] x86/fred: FRED initialization code

On Sat, Mar 18, 2023 at 02:33:30PM +0800, Lai Jiangshan wrote:
> If there is no other concrete reason other than overflowing for
> assigning NMI and #DB with a stack level > 0, #VE should also
> be assigned with a stack level > 0, and #BP too. #VE can happen
> anytime and anywhere, so it is subject to overflowing too.

So #BP needs the stack-gap (redzone) for text_poke_bp().

#BP can end up in kprobes which can then end up in ftrace/perf,
depending on how it's all wired up.

#VE is currently a trainwreck vs NMI/MCE, but I think FRED solves the
worst of that. I'm not exactly sure how deep the #VE handler goes.