Re: [PATCH] Using the tlb flush util function where applicable

[Liang Chen <liangchen.linux@gmail.com>]

On 09/15/2014 03:33 PM, Radim Krčmář wrote:
> 2014-09-12 17:06-0400, Liang Chen:
>> Using kvm_mmu_flush_tlb as the other places to make sure vcpu
>>  stat is incremented
>>
>> Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
>> ---
> Good catch.
>
>>  arch/x86/kvm/vmx.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index bfe11cf..439682e 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -1810,7 +1810,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>  		struct desc_ptr *gdt = &__get_cpu_var(host_gdt);
>>  		unsigned long sysenter_esp;
>>  
>> -		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
>> +		kvm_mmu_flush_tlb(vcpu);
>>  		local_irq_disable();
>>  		crash_disable_local_vmclear(cpu);
>>  
> And to hijack this thread ...
> I noticed three other deficits in stat.tlb_flush, patch below.
>
> Do you prefer the current behavior?

Yeah, you are right. I think the patch below gives a more thorough solution to
make sure the counter really shows the number of tlb flushes - not the time 
kvm_mmu_flush_tlb is called. Thanks!

> --- 8< ---
> KVM: x86: count actual tlb flushes
>
> - we count KVM_REQ_TLB_FLUSH requests, not actual flushes
>   (KVM can have multiple requests for one flush)
> - flushes from kvm_flush_remote_tlbs aren't counted
> - it's easy to make a direct request by mistake
>
> Solve these by postponing the counting to kvm_check_request().
>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
> (And what about a possible followup patch that replaces
>  kvm_mmu_flush_tlb() with kvm_make_request() again?
>  It would free the namespace a bit and we could call something
>  similarly named from vcpu_enter_guest() to do the job.)

That seems good. I can take the labor to make the followup patch ;)

Thanks,
Liang Chen

> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 9314678..b41fd97 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3452,7 +3452,6 @@ static void nonpaging_init_context(struct kvm_vcpu *vcpu,
>  
>  void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu)
>  {
> -	++vcpu->stat.tlb_flush;
>  	kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
>  }
>  EXPORT_SYMBOL_GPL(kvm_mmu_flush_tlb);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 916e895..0f0ad08 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6041,8 +6041,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  		}
>  		if (kvm_check_request(KVM_REQ_MMU_SYNC, vcpu))
>  			kvm_mmu_sync_roots(vcpu);
> -		if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu))
> +		if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu)) {
> +			++vcpu->stat.tlb_flush;
>  			kvm_x86_ops->tlb_flush(vcpu);
> +		}
>  		if (kvm_check_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu)) {
>  			vcpu->run->exit_reason = KVM_EXIT_TPR_ACCESS;
>  			r = 0;