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

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Message-ID: <20230320164431.GQ2194297@hirez.programming.kicks-ass.net>
Date:   Mon, 20 Mar 2023 17:44:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Lai Jiangshan <jiangshanlai@...il.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 Fri, Mar 17, 2023 at 02:32:28PM -0700, H. Peter Anvin wrote:
> The purpose of separate stacks for NMI, #DB and #MC *in the kernel*
> (remember that user space faults are always taken on stack level 0) is
> to avoid overflowing the kernel stack. #DB in the kernel would imply
> the use of a kernel debugger.

Perf (and through it bpf) also has access to #DB. They can set
breakpoints on kernel instructions/memory just fine provided permission
etc.