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

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Date:   Tue, 21 Mar 2023 00:13:34 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>
CC:     Lai Jiangshan <jiangshanlai@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: RE: [PATCH v5 22/34] x86/fred: FRED initialization code

> > 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.

So they are still *kernel* debuggers :)