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Subject[RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit
Date
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();
+ }
}

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
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