Marcelo Tosatti wrote:
> On Tue, Sep 01, 2009 at 12:44:08PM +0300, Avi Kivity wrote:
>> Instead of saving the debug registers from the processor to a kvm data
>> structure, rely in the debug registers stored in the thread structure.
>> This allows us not to save dr6 and dr7.
>>
>> Reduces lightweight vmexit cost by 350 cycles, or 11 percent.
>
> Is this kgdb safe?
Nope, kgdb writes directly to the debug registers.
I vaguely recall someone trying to push a debug register management
framework. Did it hit mainline in the meantime? I do not find any trace
on quick glance, at least not in kgdb.
Jan
>
>> Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
>> ---
>> arch/x86/include/asm/kvm_host.h | 3 ---
>> arch/x86/kvm/x86.c | 22 +++++++---------------
>> 2 files changed, 7 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 6046e6f..45226f0 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -362,9 +362,6 @@ struct kvm_vcpu_arch {
>> u32 pat;
>>
>> int switch_db_regs;
>> - unsigned long host_db[KVM_NR_DB_REGS];
>> - unsigned long host_dr6;
>> - unsigned long host_dr7;
>> unsigned long db[KVM_NR_DB_REGS];
>> unsigned long dr6;
>> unsigned long dr7;
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 891234b..9e3acbd 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -3627,14 +3627,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>
>> kvm_guest_enter();
>>
>> - get_debugreg(vcpu->arch.host_dr6, 6);
>> - get_debugreg(vcpu->arch.host_dr7, 7);
>> if (unlikely(vcpu->arch.switch_db_regs)) {
>> - get_debugreg(vcpu->arch.host_db[0], 0);
>> - get_debugreg(vcpu->arch.host_db[1], 1);
>> - get_debugreg(vcpu->arch.host_db[2], 2);
>> - get_debugreg(vcpu->arch.host_db[3], 3);
>> -
>> set_debugreg(0, 7);
>> set_debugreg(vcpu->arch.eff_db[0], 0);
>> set_debugreg(vcpu->arch.eff_db[1], 1);
>> @@ -3645,15 +3638,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>> trace_kvm_entry(vcpu->vcpu_id);
>> kvm_x86_ops->run(vcpu);
>>
>> - if (unlikely(vcpu->arch.switch_db_regs)) {
>> - set_debugreg(0, 7);
>> - set_debugreg(vcpu->arch.host_db[0], 0);
>> - set_debugreg(vcpu->arch.host_db[1], 1);
>> - set_debugreg(vcpu->arch.host_db[2], 2);
>> - set_debugreg(vcpu->arch.host_db[3], 3);
>> + if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) {
>> + set_debugreg(current->thread.debugreg0, 0);
>> + set_debugreg(current->thread.debugreg1, 1);
>> + set_debugreg(current->thread.debugreg2, 2);
>> + set_debugreg(current->thread.debugreg3, 3);
>> + set_debugreg(current->thread.debugreg6, 6);
>> + set_debugreg(current->thread.debugreg7, 7);
>> }
>> - set_debugreg(vcpu->arch.host_dr6, 6);
>> - set_debugreg(vcpu->arch.host_dr7, 7);
>>
>> set_bit(KVM_REQ_KICK, &vcpu->requests);
>> local_irq_enable();
>> --
>> 1.6.4.1
--
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux
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