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Subject: Re: [PATCH v2 1/3] KVM: X86: Rename DR6_INIT to DR6_ACTIVE_LOW
To:     Xiaoyao Li <xiaoyao.li@intel.com>,
        Chenyi Qiang <chenyi.qiang@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210202090433.13441-1-chenyi.qiang@intel.com>
 <20210202090433.13441-2-chenyi.qiang@intel.com>
 <3db069ba-b4e0-1288-ec79-66ac44938682@redhat.com>
 <6678520f-e69e-6116-88c9-e9d6cd450934@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <ea9eaa84-999b-82cb-ef40-66fde361704d@redhat.com>
Date:   Tue, 2 Feb 2021 17:05:04 +0100
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On 02/02/21 16:02, Xiaoyao Li wrote:
> On 2/2/2021 10:49 PM, Paolo Bonzini wrote:
>> On 02/02/21 10:04, Chenyi Qiang wrote:
>>>
>>>  #define DR6_FIXED_1    0xfffe0ff0
>>> -#define DR6_INIT    0xffff0ff0
>>> +/*
>>> + * DR6_ACTIVE_LOW is actual the result of DR6_FIXED_1 | 
>>> ACTIVE_LOW_BITS.
>>> + * We can regard all the current FIXED_1 bits as active_low bits even
>>> + * though in no case they will be turned into 0. But if they are 
>>> defined
>>> + * in the future, it will require no code change.
>>> + * At the same time, it can be served as the init/reset value for DR6.
>>> + */
>>> +#define DR6_ACTIVE_LOW    0xffff0ff0
>>>  #define DR6_VOLATILE    0x0001e00f
>>>
>>
>> Committed with some changes in the wording of the comment.
>>
>> Also, DR6_FIXED_1 is (DR6_ACTIVE_LOW & ~DR6_VOLATILE).
> 
> Maybe we can add BUILD_BUG_ON() to make sure the correctness?

We can even

#define DR_FIXED_1  (DR6_ACTIVE_LOW & ~DR6_VOLATILE)

directly.  I have pushed this patch to kvm/queue, but the other two will 
have to wait for Fenghua's bare metal support.

Paolo