linux-kernel - Re: [PATCH v1 0/3] x86/traps: Fix DR6/DR7 inintialization

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Message-ID: <457250dc-5e3f-498f-8b71-6ea4879f91af@zytor.com>
Date: Fri, 13 Jun 2025 00:37:46 -0700
From: Xin Li <xin@...or.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, seanjc@...gle.com, pbonzini@...hat.com,
        brgerst@...il.com, tony.luck@...el.com, fenghuay@...dia.com
Subject: Re: [PATCH v1 0/3] x86/traps: Fix DR6/DR7 inintialization

On 6/13/2025 12:18 AM, Peter Zijlstra wrote:
> On Fri, Jun 13, 2025 at 12:01:14AM -0700, Xin Li (Intel) wrote:
>>
>> Since only BLD-induced #DB exceptions clear DR6.BLD and other debug
>> exceptions leave it unchanged, even if the first #DB is unrelated to
>> BLD, DR6.BLD is still cleared.  As a result, such a first #DB is
>> misinterpreted as a BLD #DB, and a false warning is triggerred.
>>
>>
>> Fix the bug by initializing DR6 by writing its architectural reset
>> value at boot time.
>>
>>
>> DR7 suffers from a similar issue.  We apply the same fix.
> 
> Bah, this DR6 polarity is a pain in the behind for sure. Patches look
> good, except I'm really not a fan of using those 'names'. But I'll not
> object too much of others like it.

Let's see if there will be more objections :)