From: Xiaoyao Li <xiaoyao.li@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Chenyi Qiang <chenyi.qiang@intel.com>,
Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit
Date: Thu, 28 Jan 2021 15:17:19 +0800 [thread overview]
Message-ID: <ec623f67-d7b7-2d9a-1610-4da7702288b1@intel.com> (raw)
In-Reply-To: <6bf8fc0d-ad7d-0282-9dcc-695f16af0715@redhat.com>
On 1/27/2021 6:04 PM, Paolo Bonzini wrote:
> On 27/01/21 04:41, Xiaoyao Li wrote:
>> 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.
>
> "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.
> Paolo
>
>>>> - dr6 |= DR6_BD | DR6_RTM;
>>>> + dr6 |= DR6_BD | DR6_RTM | DR6_BUS_LOCK;
>>>
>>> dr6 |= DR6_BD | DR6_ACTIVE_LOW;
>>>
>>
>>
>
next prev parent reply other threads:[~2021-01-28 7:20 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 6:49 [RESEND PATCH 0/2] Add KVM support for bus lock debug exception Chenyi Qiang
2021-01-08 6:49 ` [RESEND PATCH 1/2] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit Chenyi Qiang
2021-01-08 16:38 ` kernel test robot
2021-01-26 16:31 ` Paolo Bonzini
2021-01-27 1:48 ` Chenyi Qiang
2021-01-27 3:41 ` Xiaoyao Li
2021-01-27 10:04 ` Paolo Bonzini
2021-01-28 7:17 ` Xiaoyao Li [this message]
2021-01-28 7:25 ` Paolo Bonzini
2021-01-28 7:41 ` Xiaoyao Li
2021-01-08 6:49 ` [RESEND PATCH 2/2] KVM: X86: Expose bus lock debug exception to guest Chenyi Qiang
2021-01-08 18:16 ` kernel test robot
2021-01-26 16:33 ` Paolo Bonzini
2021-01-27 0:57 ` Chenyi Qiang
2021-01-27 12:31 ` Paolo Bonzini
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