[RFC PATCH v2 2/4] KVM: x86: Add KVM exit for IOAPIC EOIs

Steve Rutherford
2015-05-15T02:52:23Z

Adds KVM_EXIT_IOAPIC_EOI which allows the kernel to EOI
level-triggered IOAPIC interrupts.

Uses a per VCPU exit bitmap to decide whether or not the IOAPIC needs
to be informed (which is identical to the EOI_EXIT_BITMAP field used
by modern x86 processors, but can also be used to elide kvm IOAPIC EOI
exits on older processors).

[Note: A prototype using ResampleFDs found that decoupling the EOI
from the VCPU's thread made it possible for the VCPU to not see a
recent EOI after reentering the guest. This does not match real
hardware.]

Compile tested for Intel x86.

Signed-off-by: Steve Rutherford <srutherford@google.com>
---
Documentation/virtual/kvm/api.txt | 10 ++++++++++
arch/x86/include/asm/kvm_host.h | 3 +++
arch/x86/kvm/lapic.c | 9 +++++++++
arch/x86/kvm/x86.c | 11 +++++++++++
include/linux/kvm_host.h | 1 +
include/uapi/linux/kvm.h | 5 +++++
6 files changed, 39 insertions(+)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 9a43d42..6ab2a3f7 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3271,6 +3271,16 @@ Valid values for 'type' are:
*/
__u64 kvm_valid_regs;
__u64 kvm_dirty_regs;
+
+ /* KVM_EXIT_IOAPIC_EOI */
+ struct {
+ __u8 vector;
+ } eoi;
+
+Indicates that an eoi of a level triggered IOAPIC interrupt on vector has
+occurred, which should be handled by the userspace IOAPIC. Triggers when
+the Irqchip has been split between userspace and the kernel.
+
union {
struct kvm_sync_regs regs;
char padding[1024];
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3ddc134..b1978f1 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -539,6 +539,9 @@ struct kvm_vcpu_arch {
struct {
bool pv_unhalted;
} pv;
+
+ u64 eoi_exit_bitmaps[4];
+ int pending_ioapic_eoi;
};

struct kvm_lpage_info {
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index bc392a6..42fada6f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -860,6 +860,15 @@ int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)

static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector)
{
+ if (irqchip_split(apic->vcpu->kvm)) {
+ if (test_bit(vector,
+ (void *) apic->vcpu->arch.eoi_exit_bitmaps)) {
+ apic->vcpu->arch.pending_ioapic_eoi = vector;
+ kvm_make_request(KVM_REQ_IOAPIC_EOI_EXIT, apic->vcpu);
+ }
+ return;
+ }
+
if (kvm_ioapic_handles_vector(apic->vcpu->kvm, vector)) {
int trigger_mode;
if (apic_test_vector(vector, apic->regs + APIC_TMR))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fc347fa..e7377df 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6324,6 +6324,17 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_handle_pmu_event(vcpu);
if (kvm_check_request(KVM_REQ_PMI, vcpu))
kvm_deliver_pmi(vcpu);
+ if (kvm_check_request(KVM_REQ_IOAPIC_EOI_EXIT, vcpu)) {
+ BUG_ON(vcpu->arch.pending_ioapic_eoi > 255);
+ if (test_bit(vcpu->arch.pending_ioapic_eoi,
+ (void *) vcpu->arch.eoi_exit_bitmaps)) {
+ vcpu->run->exit_reason = KVM_EXIT_IOAPIC_EOI;
+ vcpu->run->eoi.vector =
+ vcpu->arch.pending_ioapic_eoi;
+ r = 0;
+ goto out;
+ }
+ }
if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu))
vcpu_scan_ioapic(vcpu);
if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 277b7a1..cef20ad 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -134,6 +134,7 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQ_ENABLE_IBS 23
#define KVM_REQ_DISABLE_IBS 24
#define KVM_REQ_APIC_PAGE_RELOAD 25
+#define KVM_REQ_IOAPIC_EOI_EXIT 26

#define KVM_USERSPACE_IRQ_SOURCE_ID 0
#define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 1e6f6c3..826a08d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -183,6 +183,7 @@ struct kvm_s390_skeys {
#define KVM_EXIT_EPR 23
#define KVM_EXIT_SYSTEM_EVENT 24
#define KVM_EXIT_S390_STSI 25
+#define KVM_EXIT_IOAPIC_EOI 26

/* For KVM_EXIT_INTERNAL_ERROR */
/* Emulate instruction failed. */
@@ -329,6 +330,10 @@ struct kvm_run {
__u8 sel1;
__u16 sel2;
} s390_stsi;
+ /* KVM_EXIT_IOAPIC_EOI */
+ struct {
+ __u8 vector;
+ } eoi;
/* Fix the size of the union. */
char padding[256];
};
--
2.2.0.rc0.207.ga3a616c