lkml.org 
[lkml]   [2016]   [Jun]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit
From
Date


On 16/06/2016 18:43, David Matlack wrote:
> On Thu, Jun 16, 2016 at 1:21 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> This gains ~20 clock cycles per vmexit. On Intel there is no need
>> anymore to enable the interrupts in vmx_handle_external_intr, since we
>> are using the "acknowledge interrupt on exit" feature. AMD needs to do
>> that temporarily, and must be careful to avoid the interrupt shadow.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>> arch/x86/kvm/svm.c | 6 ++++++
>> arch/x86/kvm/vmx.c | 4 +---
>> arch/x86/kvm/x86.c | 11 ++---------
>> 3 files changed, 9 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 5ff292778110..5bfdbbf1ce79 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -4935,6 +4935,12 @@ out:
>> static void svm_handle_external_intr(struct kvm_vcpu *vcpu)
>> {
>> local_irq_enable();
>> + /*
>> + * We must execute an instruction with interrupts enabled, so
>> + * the "cli" doesn't fall right on the interrupt shadow.
>> + */
>> + asm("nop");
>> + local_irq_disable();
>> }
>>
>> static void svm_sched_in(struct kvm_vcpu *vcpu, int cpu)
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 4e9657730bf6..a46bce9e3683 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -8544,7 +8544,6 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
>> "push %[sp]\n\t"
>> #endif
>> "pushf\n\t"
>> - "orl $0x200, (%%" _ASM_SP ")\n\t"
>> __ASM_SIZE(push) " $%c[cs]\n\t"
>> "call *%[entry]\n\t"
>> :
>> @@ -8557,8 +8556,7 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
>> [ss]"i"(__KERNEL_DS),
>> [cs]"i"(__KERNEL_CS)
>> );
>> - } else
>> - local_irq_enable();
>> + }
>
> If you make the else case the same as svm_handle_external_intr, can we
> avoid requiring ack-intr-on-exit?

Yes, but the sti/nop/cli would be useless if ack-intr-on-exit is
available. It's a bit ugly, so I RFCed the bold thing instead.

Are you thinking of some distros in particular that lack nested
ack-intr-on-exit? All processors have it as far as I know.

Paolo


>> }
>>
>> static bool vmx_has_high_real_mode_segbase(void)
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 7e3041ef050f..cc741b68139c 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -6706,21 +6706,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>
>> kvm_put_guest_xcr0(vcpu);
>>
>> - /* Interrupt is enabled by handle_external_intr() */
>> kvm_x86_ops->handle_external_intr(vcpu);
>>
>> ++vcpu->stat.exits;
>>
>> - /*
>> - * We must have an instruction between local_irq_enable() and
>> - * kvm_guest_exit(), so the timer interrupt isn't delayed by
>> - * the interrupt shadow. The stat.exits increment will do nicely.
>> - * But we need to prevent reordering, hence this barrier():
>> - */
>> - barrier();
>> -
>> - kvm_guest_exit();
>> + __kvm_guest_exit();
>>
>> + local_irq_enable();
>> preempt_enable();
>>
>> vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
>> --
>> 1.8.3.1
>>

\
 
 \ /
  Last update: 2016-06-16 19:21    [W:0.058 / U:1.956 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site