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        id 1hCVxc-0004gT-Hj; Fri, 05 Apr 2019 23:01:16 +0200
Date:   Fri, 5 Apr 2019 23:01:16 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [patch V2 19/29] x86/exceptions: Split debug IST stack
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On Fri, 5 Apr 2019, Sean Christopherson wrote:
> On Fri, Apr 05, 2019 at 05:07:17PM +0200, Thomas Gleixner wrote:
> > +	/*
> > +	 * Note, this covers the guard page between DB and DB1 as well to
> > +	 * avoid two checks. But by all means @addr can never point into
> > +	 * the guard page.
> > +	 */
> > +	return addr > bot && addr < top;
> 
> Isn't this an off by one error?  I.e. "return addr >= bot && addr < top".
> %rsp == bot is technically still in the DB1 stack even though the next
> PUSH/CALL will explode on the guard page.

Right you are.