Messages in this thread | | | Subject | Re: [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit | From | Xiaoyao Li <> | Date | Thu, 28 Jan 2021 15:41:46 +0800 |
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On 1/28/2021 3:25 PM, Paolo Bonzini wrote: > 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.
Fair enough.
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