Re: [PATCH v2 8/9] KVM: x86, SVM: isolate vcpu->arch.dr6 from vmcb->save.dr6

From: Paolo Bonzini
Date: Sat May 09 2020 - 09:28:51 EST


On 08/05/20 17:32, Peter Xu wrote:
> On Fri, May 08, 2020 at 12:33:57AM +0200, Paolo Bonzini wrote:
>> On 07/05/20 21:28, Peter Xu wrote:
>>>> - svm->vcpu.arch.dr6 = dr6;
>>>> + WARN_ON(svm->vcpu.arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT);
>>>> + svm->vcpu.arch.dr6 &= ~(DR_TRAP_BITS | DR6_RTM);
>>>> + svm->vcpu.arch.dr6 |= dr6 & ~DR6_FIXED_1;
>>> I failed to figure out what the above calculation is going to do...
>>
>> The calculation is merging the cause of the #DB with the guest DR6.
>> It's basically the same effect as kvm_deliver_exception_payload.
>
> Shall we introduce a helper for both kvm_deliver_exception_payload and here
> (e.g. kvm_merge_dr6)? Also, wondering whether this could be a bit easier to
> follow by defining:

It would make sense indeed but I plan to get rid of this in 5.9 (so in
about a month), as explained in the comment.

Paolo