linux-kernel - Re: [PATCH v5 20/34] x86/fred: add a machine check entry stub for FRED

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Message-ID: <20230320160021.GP2194297@hirez.programming.kicks-ass.net>
Date:   Mon, 20 Mar 2023 17:00:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Xin Li <xin3.li@...el.com>
Cc:     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, hpa@...or.com,
        andrew.cooper3@...rix.com, seanjc@...gle.com, pbonzini@...hat.com,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH v5 20/34] x86/fred: add a machine check entry stub for
 FRED

On Mon, Mar 06, 2023 at 06:39:32PM -0800, Xin Li wrote:
> Add a machine check entry stub for FRED.
> 
> Unlike IDT, no need to save/restore dr7 in FRED machine check handler.

Given how fragile MCE is, the question should be, do we ever want hw
breakpoints to happen while it is running?

If the hw-breakpoint handler trips on the same memory fail that got us
into the mce the first time, we're dead.