linux-kernel - Re: [RFC PATCH 1/3] kvm: x86: Rename KVM_DEBUGREG_RELOAD to KVM_DEBUGREG_NEED

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Message-ID: <f2b2c045-ab64-fe0e-6108-45de51ed9be9@intel.com>
Date:   Fri, 24 Apr 2020 21:28:53 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Nadav Amit <namit@...technion.ac.il>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] kvm: x86: Rename KVM_DEBUGREG_RELOAD to
 KVM_DEBUGREG_NEED_RELOAD

On 4/24/2020 3:09 AM, Sean Christopherson wrote:
> On Thu, Apr 16, 2020 at 06:15:07PM +0800, Xiaoyao Li wrote:
>> To make it more clear that the flag means DRn (except DR7) need to be
>> reloaded before vm entry.
>>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
>> ---
>>   arch/x86/include/asm/kvm_host.h | 2 +-
>>   arch/x86/kvm/x86.c              | 6 +++---
>>   2 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index c7da23aed79a..f465c76e6e5a 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -511,7 +511,7 @@ struct kvm_pmu_ops;
>>   enum {
>>   	KVM_DEBUGREG_BP_ENABLED = 1,
>>   	KVM_DEBUGREG_WONT_EXIT = 2,
>> -	KVM_DEBUGREG_RELOAD = 4,
>> +	KVM_DEBUGREG_NEED_RELOAD = 4,
> 
> My vote would be for KVM_DEBUGREG_DIRTY  Any bit that is set switch_db_regs
> triggers a reload, whereas I would expect a RELOAD flag to be set _every_
> time a load is needed and thus be the only bit that's checked
> 

That's what I intended to do with this series, apparently I failed it. :(

>>   };
>>   
>>   struct kvm_mtrr_range {
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index de77bc9bd0d7..cce926658d10 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1067,7 +1067,7 @@ static void kvm_update_dr0123(struct kvm_vcpu *vcpu)
>>   	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)) {
>>   		for (i = 0; i < KVM_NR_DB_REGS; i++)
>>   			vcpu->arch.eff_db[i] = vcpu->arch.db[i];
>> -		vcpu->arch.switch_db_regs |= KVM_DEBUGREG_RELOAD;
>> +		vcpu->arch.switch_db_regs |= KVM_DEBUGREG_NEED_RELOAD;
>>   	}
>>   }
>>   
>> @@ -8407,7 +8407,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>   		set_debugreg(vcpu->arch.eff_db[2], 2);
>>   		set_debugreg(vcpu->arch.eff_db[3], 3);
>>   		set_debugreg(vcpu->arch.dr6, 6);
>> -		vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD;
>> +		vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_NEED_RELOAD;
>>   	}
>>   
>>   	kvm_x86_ops.run(vcpu);
>> @@ -8424,7 +8424,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>   		kvm_update_dr0123(vcpu);
>>   		kvm_update_dr6(vcpu);
>>   		kvm_update_dr7(vcpu);
>> -		vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD;
>> +		vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_NEED_RELOAD;
> 
> This is the path that I think would really benefit from DIRTY, it took me
> several reads to catch that kvm_update_dr0123() will set RELOAD.
> 
>>   	}
>>   
>>   	/*
>> -- 
>> 2.20.1
>>