linux-kernel - Re: [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of DR6_BUS

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Message-ID: <5f3089a2-5a5c-a839-9ed9-471c404738a3@intel.com>
Date:   Wed, 27 Jan 2021 11:41:21 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Chenyi Qiang <chenyi.qiang@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of
 DR6_BUS_LOCK bit

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;
>