[PATCH] KVM: x86: Convert INIT and SIPI signals into synchronously handled requests

Jan Kiszka
2013-03-03T20:21:48Z

From: Jan Kiszka <jan.kiszka@siemens.com>

A VCPU sending INIT or SIPI to some other VCPU races for setting the
remote VCPU's mp_state. When we were unlucky, KVM_MP_STATE_INIT_RECEIVED
was overwritten by kvm_emulate_halt and, thus, got lost.

Fix this by raising requests on the sender side that will then be
handled synchronously over the target VCPU context.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Turned out to be simpler than expected. I'm no longer able to reproduce
the race I saw before.

arch/x86/kvm/lapic.c | 9 ++++-----
arch/x86/kvm/x86.c | 16 +++++++++++++++-
include/linux/kvm_host.h | 2 ++
3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 02b51dd..be1e37a 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -731,8 +731,7 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
case APIC_DM_INIT:
if (!trig_mode || level) {
result = 1;
- vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
- kvm_make_request(KVM_REQ_EVENT, vcpu);
+ kvm_make_request(KVM_REQ_INIT, vcpu);
kvm_vcpu_kick(vcpu);
} else {
apic_debug("Ignoring de-assert INIT to vcpu %d\n",
@@ -743,11 +742,11 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
case APIC_DM_STARTUP:
apic_debug("SIPI to vcpu %d vector 0x%02x\n",
vcpu->vcpu_id, vector);
- if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
+ if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED ||
+ test_bit(KVM_REQ_INIT, &vcpu->requests)) {
result = 1;
vcpu->arch.sipi_vector = vector;
- vcpu->arch.mp_state = KVM_MP_STATE_SIPI_RECEIVED;
- kvm_make_request(KVM_REQ_EVENT, vcpu);
+ kvm_make_request(KVM_REQ_SIPI, vcpu);
kvm_vcpu_kick(vcpu);
}
break;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d0cf737..8c8843c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5641,6 +5641,18 @@ static void update_eoi_exitmap(struct kvm_vcpu *vcpu)
kvm_x86_ops->load_eoi_exitmap(vcpu, eoi_exit_bitmap);
}

+static bool kvm_check_init_and_sipi(struct kvm_vcpu *vcpu)
+{
+ if (kvm_check_request(KVM_REQ_INIT, vcpu))
+ vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
+ if (kvm_check_request(KVM_REQ_SIPI, vcpu) &&
+ vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
+ vcpu->arch.mp_state = KVM_MP_STATE_SIPI_RECEIVED;
+ return true;
+ }
+ return false;
+}
+
static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
{
int r;
@@ -5649,6 +5661,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
bool req_immediate_exit = 0;

if (vcpu->requests) {
+ kvm_check_init_and_sipi(vcpu);
if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
kvm_mmu_unload(vcpu);
if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
@@ -6977,10 +6990,11 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,

int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
{
+ if (kvm_check_init_and_sipi(vcpu))
+ return 1;
return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
!vcpu->arch.apf.halted)
|| !list_empty_careful(&vcpu->async_pf.done)
- || vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED
|| atomic_read(&vcpu->arch.nmi_queued) ||
(kvm_arch_interrupt_allowed(vcpu) &&
kvm_cpu_has_interrupt(vcpu));
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 722cae7..1a191c9 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -124,6 +124,8 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQ_MCLOCK_INPROGRESS 20
#define KVM_REQ_EPR_EXIT 21
#define KVM_REQ_EOIBITMAP 22
+#define KVM_REQ_INIT 23
+#define KVM_REQ_SIPI 24

#define KVM_USERSPACE_IRQ_SOURCE_ID 0
#define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
--
1.7.3.4