KVM: host side for eoi optimization

Implementation of PV EOI using shared memory.
This reduces the number of exits an interrupt
causes as much as by half.

The idea is simple: there's a bit, per APIC, in guest memory,
that tells the guest that it does not need EOI.
We set it before injecting an interrupt and clear
before injecting a nested one. Guest tests it using
a test and clear operation - this is necessary
so that host can detect interrupt nesting -
and if set, it can skip the EOI MSR.

There's a new MSR to set the address of said register
in guest memory. Otherwise not much changed:
- Guest EOI is not required
- Register is tested & ISR is automatically cleared on exit

For testing results see description of previous patch
'kvm_para: guest side for eoi avoidance'.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7ea0f611bc89..8eacb2e64560 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -795,6 +795,7 @@ static u32 msrs_to_save[] = {
         MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
         HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
         HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
+        MSR_KVM_PV_EOI_EN,
         MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
         MSR_STAR,
 #ifdef CONFIG_X86_64
@@ -1653,6 +1654,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
                 kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
 
                 break;
+        case MSR_KVM_PV_EOI_EN:
+                if (kvm_lapic_enable_pv_eoi(vcpu, data))
+                        return 1;
+                break;
 
         case MSR_IA32_MCG_CTL:
         case MSR_IA32_MCG_STATUS:
@@ -5394,6 +5399,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 cancel_injection:
         kvm_x86_ops->cancel_injection(vcpu);
+        if (unlikely(vcpu->arch.apic_attention))
+                kvm_lapic_sync_from_vapic(vcpu);
 out:
         return r;
 }