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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id l16sm2588861edw.10.2021.01.27.23.25.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Jan 2021 23:25:17 -0800 (PST) Subject: Re: [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit To: Xiaoyao Li , Chenyi Qiang , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210108064924.1677-1-chenyi.qiang@intel.com> <20210108064924.1677-2-chenyi.qiang@intel.com> <5f3089a2-5a5c-a839-9ed9-471c404738a3@intel.com> <6bf8fc0d-ad7d-0282-9dcc-695f16af0715@redhat.com> From: Paolo Bonzini Message-ID: Date: Thu, 28 Jan 2021 08:25:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/01/21 08:17, Xiaoyao Li wrote: >> >> "Active low" means that the bit is usually 1 and goes to 0 when the >> condition (such as RTM or bus lock) happens.  For almost all those DR6 >> bits the value is in fact always 1, but if they are defined in the >> future it will require no code change. > > Why not keep use DR6_INIT, or DR6_RESET_VALUE? or any other better name. > > It's just the default clear value of DR6 that no debug condition is hit. I preferred "DR6_ACTIVE_LOW" because the value is used only once or twice to initialize dr6, and many times to invert those bits. For example: vcpu->arch.dr6 &= ~DR_TRAP_BITS; vcpu->arch.dr6 |= DR6_ACTIVE_LOW; vcpu->arch.dr6 |= payload; vcpu->arch.dr6 ^= payload & DR6_ACTIVE_LOW; payload = vcpu->arch.dr6; payload &= ~DR6_BT; payload ^= DR6_ACTIVE_LOW; The name conveys that it's not just the initialization value; it's also the XOR mask between the #DB exit qualification (which we also use as the "payload") and DR6. Paolo