[PATCH v4 04/11] KVM: arm/arm64: properly use vcpu requests

Andrew Jones
2017-05-16T02:20:28Z

arm/arm64 already has one VCPU request used when setting pause,
but it doesn't properly check requests in VCPU RUN. Check it
and also make sure we set vcpu->mode at the appropriate time
(before the check) and with the appropriate barriers. See
Documentation/virtual/kvm/vcpu-requests.rst. Also make sure we
don't leave any vcpu requests we don't intend to handle later
set in the request bitmap. If we don't clear them, then
kvm_request_pending() may return true when it shouldn't.

Using VCPU requests properly fixes a small race where pause
could get set just as a VCPU was entering guest mode.

Signed-off-by: Andrew Jones <drjones@redhat.com>
---
arch/arm/kvm/handle_exit.c | 1 +
arch/arm64/kvm/handle_exit.c | 1 +
virt/kvm/arm/arm.c | 14 ++++++++++++--
virt/kvm/arm/psci.c | 1 +
4 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kvm/handle_exit.c b/arch/arm/kvm/handle_exit.c
index 5fd7968cdae9..a2b4f7b82356 100644
--- a/arch/arm/kvm/handle_exit.c
+++ b/arch/arm/kvm/handle_exit.c
@@ -72,6 +72,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
trace_kvm_wfx(*vcpu_pc(vcpu), false);
vcpu->stat.wfi_exit_stat++;
kvm_vcpu_block(vcpu);
+ kvm_clear_request(KVM_REQ_UNHALT, vcpu);
}

kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index fa1b18e364fc..17d8a1677a0b 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -89,6 +89,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
trace_kvm_wfx_arm64(*vcpu_pc(vcpu), false);
vcpu->stat.wfi_exit_stat++;
kvm_vcpu_block(vcpu);
+ kvm_clear_request(KVM_REQ_UNHALT, vcpu);
}

kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 3c387fdc4a9e..138212605ad9 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -546,6 +546,7 @@ void kvm_arm_resume_guest(struct kvm *kvm)

kvm_for_each_vcpu(i, vcpu, kvm) {
vcpu->arch.pause = false;
+ kvm_clear_request(KVM_REQ_VCPU_EXIT, vcpu);
swake_up(kvm_arch_vcpu_wq(vcpu));
}
}
@@ -638,8 +639,18 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
run->exit_reason = KVM_EXIT_INTR;
}

+ /*
+ * Ensure we set mode to IN_GUEST_MODE after we disable
+ * interrupts and before the final VCPU requests check.
+ * See the comment in kvm_vcpu_exiting_guest_mode() and
+ * Documentation/virtual/kvm/vcpu-requests.rst
+ */
+ smp_store_mb(vcpu->mode, IN_GUEST_MODE);
+
if (ret <= 0 || need_new_vmid_gen(vcpu->kvm) ||
- vcpu->arch.power_off || vcpu->arch.pause) {
+ kvm_request_pending(vcpu) ||
+ vcpu->arch.power_off || vcpu->arch.pause) {
+ vcpu->mode = OUTSIDE_GUEST_MODE;
local_irq_enable();
kvm_pmu_sync_hwstate(vcpu);
kvm_timer_sync_hwstate(vcpu);
@@ -655,7 +666,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
*/
trace_kvm_entry(*vcpu_pc(vcpu));
guest_enter_irqoff();
- vcpu->mode = IN_GUEST_MODE;

ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);

diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
index a08d7a93aebb..f68be2cc6256 100644
--- a/virt/kvm/arm/psci.c
+++ b/virt/kvm/arm/psci.c
@@ -57,6 +57,7 @@ static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
* for KVM will preserve the register state.
*/
kvm_vcpu_block(vcpu);
+ kvm_clear_request(KVM_REQ_UNHALT, vcpu);

return PSCI_RET_SUCCESS;
}
--
2.9.3