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Date:   Fri, 29 May 2020 21:02:18 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Andrew Cooper <andrew.cooper3@citrix.com>, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Lai Jiangshan <laijs@linux.alibaba.com>,
        sean.j.christopherson@intel.com, daniel.thompson@linaro.org
Subject: Re: [PATCH 1/6] x86/entry: Introduce local_db_{save,restore}()
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 <AC94E789-9EC7-4156-955C-841FF7114176@amacapital.net>
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On Fri, May 29, 2020 at 10:28:33AM -0700, Andy Lutomirski wrote:
> > +static __always_inline unsigned long local_db_save(void)
> > +{
> > +    unsigned long dr7;
> > +
> > +    get_debugreg(&dr7, 7);
> > +    dr7 ^= 0x400;
> 
> Why xor?  This seems extra confusing.

I'll do the normal mask thing ..