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.
