Re: [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit

Xiaoyao Li
2021-01-27T06:13:45Z

On 1/27/2021 12:31 AM, Paolo Bonzini wrote:
> On 08/01/21 07:49, Chenyi Qiang wrote:
>> To avoid breaking the CPUs without bus lock detection, activate the
>> DR6_BUS_LOCK bit (bit 11) conditionally in DR6_FIXED_1 bits.
>>
>> The set/clear of DR6_BUS_LOCK is similar to the DR6_RTM in DR6
>> register. The processor clears DR6_BUS_LOCK when bus lock debug
>> exception is generated. (For all other #DB the processor sets this bit
>> to 1.) Software #DB handler should set this bit before returning to the
>> interrupted task.
>>
>> For VM exit caused by debug exception, bit 11 of the exit qualification
>> is set to indicate that a bus lock debug exception condition was
>> detected. The VMM should emulate the exception by clearing bit 11 of the
>> guest DR6.
>
> Please rename DR6_INIT to DR6_ACTIVE_LOW, and then a lot of changes
> become simpler:

Paolo,

What do you want to convey with the new name DR6_ACTIVE_LOW? To be
honest, the new name is confusing to me.

>> -        dr6 |= DR6_BD | DR6_RTM;
>> +        dr6 |= DR6_BD | DR6_RTM | DR6_BUS_LOCK;
>
> dr6 |= DR6_BD | DR6_ACTIVE_LOW;
>